Bloggers and HP people waiting to tour lab

[long post 945 wds] HP held their (annual?) HP Tech Days in Fort Collins, Colorado this last week. We had presentations from a number of HP product managers and got to meet a number of new and old bloggers there.

In attendance from the blogosphere were: Alastair Cooke (@DemitasseNZ), Brian Knudtson (@bknudtson), Howard Marks (@DeepStorageNet), John Obeto (@JohnObeto), Jeff Powers (@Geekazine), Rich Schandler (@recklessop), Derek Schauland (@webjunkie), Justin Vashisht (@3cVGuy), and Matt Vogt (@MattVogt).

Craig Nunes VP of Marketing, HP Storage got up and led off the day’s discussion talking about recent results. HP disk storage is up 11% for the quarter, 3par is growing by triple digit growth (QoQ maybe YoY?) and channel sales are growing by 10%.  HP storage is gaining market share, grew 3% for the quarter.  Also, HP is #2 is shipped backup appliances (1H11).  The current focus for HP storage is in three areas:

• Invest in established platforms, MSA and EVA (with a 100K customers)
• Invest in converged storage aimed at new data centers, 3PAR, Lefthand, IBRIX and StoreOnce.
• Invest in converged systems knocking down barriers between servers, storage and networking with Virtual Systems.

Craig spent most of his time talking about converged storage. HP’s converged storage includes:

• built in autonomic storage automating operations with one pain of glass and an orchestration layer on top to oversee everything.
• scale out storage providing simpler ways to grow storage.
• built on standardized platforms using off the shelf server platform technology

Craig ended up discussing HP’s Virtual System, their response to VCE’s Vblock, NetApp’s FlexPod and Dell’s vStart Bundle.   HP’s Virtual System was announced earlier last year and has been doing well in the market.

Brad Katz, Product Manager got up next and talked about Lefthand storage solutions.  Lefthand’s portfolio now ranges from the Virtual Storage Appliance (VSA) all the way up to a P4800 SAN storage blade with P4300 and P4500 rackmountable storage systems between those two.   Lefthand systems provide a clustered, scale-out IP/SAN and NAS storage.   Cluster data is striped across all disks in all storage nodes.

The VSA runs as a virtual machine and utilizes any ESX  (direct or SAN attached) storage.  The P4800 operates as a storage blade in an HP blade server and uses storage in the blade system.  The two rackmount systems P4300 and P4500 connect to SAS attached, external disk shelves.

Steve Johnson on StoreOnce

Steve Johnson and Mat Jacoby talked next about the StoreOnce deduplicating backup appliance product line.  StoreOnce is an HP R&D Labs home grown, deduplication technology which provides balanced ingest-restore rates and memory efficient deduplication.  The current product line spans D2D25xx, D2D41xx, D2D43xx and the recently announced, B6200 backup storage blade.

StoreOnce use a variable block, 4K chunksize and a sparse index which saves on server memory size which both lead to great deduplication rates.   Most deduplication functionality is memory intensive making it hard to scale without increasing memory or using different dedupe engines across a product line.  StoreOnce’s sparse indexing fixed that issue and as such, can use the same deduplication engine across their entire product line.

JR talking about 3PAR advantages

Jim Richardson or JR, a 3PAR SE from the start, got up and discussed 3PAR.  Early on, 3PAR brought to the market three characteristics that differentiated it from other enterprise storage products:

• Multi-tennancy – today’s cloud service providers and just about anyone running enterprise storage needs to support mixed workloads on shared storage. 3PAR’s ASIC allows data to be placed on any storage node and be serviced at direct access speeds to better support these multi-application environments. 
• Thin provisioning – although certainly not the first to support thin provisioning (Iceberg was the first), 3PAR did much to popularize it.  Once again the ASIC provides automated support for thin provisioning.  
• Autonomic functionality – optimization of storage performance across nodes and tiers of storage was also helped by their ASIC’s ability to transfer data without involving processor interaction.  Also 3PAR, tried to take the drudgery out of administration by automatically wide striping and making provisioning easier.

Jim Hankins and Chris Duffy came up next and talked about the X9000 IBRIX storage system.  Ibrix has intrinsic scale out NAS support and provides automatic failover across dual processing nodes called couplets. The B6200 backup system (see above) is based on Ibrix technology.  Ibrix supports a 15PB single name space that is segmented across cluster couplets.  Ibrix also comes in a gateway configuration using shared SAN storage behind it.

HP X5000 NAS system

Robert Thompson got up and talked about the X5000 Windows Server WSS based NAS product.  It is the industry’s first two node file system with active/active clustering in a box.  As the product runs Windows Server, one can run Anti-Virus or other server applications directly on the storage and is customer maintainable. Robert pulled out every replaceable unit in the system.  Apparently the E5000, HP Storage’s Exchange Appliance is also based on the same hardware.   The two servers in the storage system are clustered together using MSCS.

HPer showing off intelligent floor tiles

In the afternoon we went on a lab tour and got to see some of HP’s storage and data center cooling technology on display.

On the second day, Mike Koponen got up and discussed HP’s Virtual System (or Vblock competitor) and Aboubacar Diare gave some of his opinions on VMware VAAI & VASA integration from his testing perspective.  Finally, Calvin Zito wrapped up the two day event and everyone (except me and a few others) went on a brewery tour.

~~~~

All in all, we had a good time with HP.  Too bad, I didn’t get to go on the New Belgium Brewery tour, perhaps next time.

Comments?

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Post tags: autonomic storage, converged storage, HP 3PAR, HP B6200, HP data center cooling technology, HP Ibrix, HP StoreOnce, HP Tech Days, HP X5000, HP X9000, Multi-tenancy

SCIESRP110726-004 (c) 2011 Silverton Consulting, All Rights Reserved

Microsoft specifies two different metrics on sequential read rates for database backup activity in their Exchange Solution Reviewed Program (ESRP) reports

• MB read/sec per database
• MB read/sec total per server

Our problem with these metrics is that they don’t say much about the storage systems performance.  Some ESRP submissions could have a single database while others can have 100s of databases.  And the same thing applies to servers, although 20 servers seems to be about the max we have seen.  So as one can see the MB/s/DB or MB/s/server can vary all over the place depending on the Exchange configuration that one uses, even for the same exact storage system.

In the above chart, we  have attempted to move beyond some of these problems and use the information supplied in the ESRP reports to aggregate DB backups across all databases.  As such, we have derived a new metric called “total database backup”.  (Pretty simple actually just multiply the MB/s/DB times the number of databases in the Exchange configuration).

A couple of problems with our approach.

• Current ESRP reports typically utilize a shadow storage system and shadow Exchange servers which host 50% of the databases and email activity. So what I am showing for those ESRP reports is what two storage systems can accomplish not one.
• Another potential way to get the same result would be to use the number of servers times the MB/sec/server metric. (But try as I might these two approaches didn’t work to get the same answer so I am using the computation above – must be the way I am recording the number of [shadow] servers).
• Although ESRP reports the average MB/sec/database to backup a single database it’s not clear that these measurements were taken while backing up all active databases at the same time, especially for those submissions with 100s of databases.

Probably the last is the most problematic critique to our new measure but may not be that harmful for smaller configurations. Nonetheless, we produced the above chart and published it in our last months review of ESRP results for the 1001 to 5000 mailbox category.

One item we discussed in our report was that numbers of disk drives didn’t seem to correlate well with high positions on this chart.  The number ten position (Fujitsu ETERNUS JX40) used over 140 disks, the number two position (Dell PowerEdge R510) had only 12 disk drives, and the number one solution (HP E5700) consisted of 56 drives, close to the average for this category.

One striking finding using this measure is that performance varies considerably from the top providing over 1600 MB/sec of database backup to the lowest of the group providing only ~800 MB/sec of backup performance. What with Exchange 2010 and lagged DAGs, some people feel that backup activity is no longer needed but we would disagree. We continue to believe that taking backups of Exchange data still makes a whole lot of sense and shouldn’t go away, ever.

It’s our hope that this or some similar follow-on metric will remove some of the Exchange configuration parameters from confounding ESRP reported storage system performance results.  We realize that this quixotic quest may never be entirely successful nevertheless we perform this duty in the hope that it will benefit today and future storage performance analysts everywhere.

Comments?

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The full ESRP report went out to our newsletter subscribers last month.  A copy of the full report will be up on the dispatches page of our website later next month. However, you can get this information now and subscribe to future newsletters to receive these reports even earlier by just emailing us at SubscribeNews@SilvertonConsulting.com?Subject=Subscribe_to_NewsletterR or using the signup form above and to the right.

As always, we welcome any suggestions on how to improve our analysis of ESRP or any of our other storage system performance discussions.

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Post tags: 1K-to-5Kmbx, Database backup performance, Dell PowerEdge R510, Email performance, ESRP, Exchange 2010, Exchange performance, Exchange Solution Reviewed Program, Fujitsu ETERNUS JX40, HP E5700

Some of the booths along the walk to the solutions pavilion highlight EMC innovation winners. Two that caught my interest included:

• Constellation computing – not quite sure how to define this but it’s distributed computing along with distributed data creation.  The intent is to move the data processing to the source of the data creation and keep the data there.  This might be very useful for applications that have many data sources and where data processing capabilities can be moved out to the nodes where the data was created. Seems highly scaleable but may depend on the ability to carve up the processing to work on the local data. I can see where compression, encryption, indexing and some statistical summarization can be done at the data creation site before it’s sent elsewhere. Sort of like both a sensor mesh with a processing nodes attached to the sensors configured as a sensor-proccessing grid.  Only one thing concerned me, there didn’t seem to be any central repository or control to this computing environment.  Probably what they intended, as the distributed solution is more adaptable and more scaleable than a centrally controlled environment.
• Developing world healthcare cloud – seemed to be all about delivering healthcare to the bottom of the pyramid.  They won EMC’s social innovation award and are working with a group in Rwanda to try to provide better healthcare to remote villages.  It’s built around OpenMRS as a backend medical record archive hosted on EMC DC powered Iomega NAS storage and uses Google’s OpenDataKit to work with the data on mobile and laptop devices.  They showed a mobile phone which could be used to create, record and retrieve healthcare information (OpenMRS records) remotely and upload it sometime later when in range of a cell tower.  The solution also supports the download of a portion of the medical center’s health record database (e.g., a “cohort” slice, think a village’s healthcare records) onto a laptop, usable offline by a healthcare provider to update and record  patient health changes onsite and remotely.  Pulling all the technology together and delivering this as an application stack usable on mobile and laptop devices with minimal IT sophistication, storage and remote/mobile access are where the challenges lie.

Went to Sanjay’s (EMC’s CIO) keynote on EMC IT’s journey to IT-as-a-Service. As you can imagine it makes extensive use of VMware’s vSphere, vCloud, and vShield capabilities primarily in a private cloud infrastructure but they seem agnostic to a build-it or buy-it approach. EMC is about 75% virtualized today, and are starting to see significant and tangible OpEx and energy savings. They designed their North Carolina data center around the vCloud architecture and now are offering business users self service portals to provision VMs and business services…

Only caught the first section of BJ’s (President of BRS) keynote but he said recent analyst data (think IDC?) said that EMC was the overall leader (>64% market share) in purpose built backup appliances (Data Domain, Disk Library, Avamar data stores, etc.).  Too bad I had to step out but he looked like he was on a roll.

Comments?

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Post tags: backup appliances, EMC, EMCWorld, grid computing, healthcare cloud, Isilon, sensor mesh

(c) 2011 Silverton Consulting, Inc., All Rights Reserved

In another assault on the tape market, EMC announced today a new Data Domain 860 Archiver appliance. This new system supports both short-term and long-term retention of backup data. This attacks one of the last bastions of significant tape use – long-term data archives.

Historically, a cheap version of archives had been the long-term retention of full backup tapes. As such, if one needed to keep data around for 5 years, one would keep all their full backup tape sets offsite, in a vault somewhere for 5 years. They could then rotate the tapes (bring them back into scratch use) after the 5 years elapsed. One problem with this – tape technology is advancing to a new generation of technology more like every 2-3 years and as such, a 5-year old tape cartridge would be at least one generation back before it could be re-used. But current tape technology always reads 2 generations and writes at least one generation back so this use would still be feasible. I would say that many tape users did something like this to create a “psuedopseudo-archive”.

On the other hand, there exists many specific archive point products that focused on one or a few application arenas such as email, records, or database archives which would extract specific data items and place them into archive. These did not generally apply outside one or a few application domains but were used to support stringent compliance requirements. The advantage of these application based archive systems is that the data was actually removed from primary storage, out of any data protection activities and placed permanently in only “archive storage”. Such data would be subject to strict retention policies and as such, would be inviolate (couldn’t be modified) and could not be deleted until formally expired.

Enter the Data Domain 860 Archiver, this system supports up to 24 disk shelves, each one of which could either be dedicated to short- or long-term data retention. Backup file data is moved within the appliance by automated policy from short- to long-term storage. Up to 4-disk shelves can be dedicated to short-term storage with the remainder considered long-term archive units.

When a long-term archive unit (disk shelf) fills up with backup data it is “sealed”, i.e., it is given all the metadata required to reconstruct its file system and deduplication domain and thus, would not require the use of other disk shelves to access its data. In this way one creates a standalone unit that contains everything needed to recover the data. Not unlike a full backup tape set which can be used in a standalone fashion to restore data.

Today, the Data Domain 860 Archiver only supports file access and DD boost data access. By doing so, the backup software is responsible for deleting data that has expired. Such data will then be absent deleted from any backups taken and as policy automation copies the backups to long-term archive units it will be missing gone from there as well.

While Data Domain’s Archiver lacks removing the data from ongoing backup streams that application based archive products can achieve, it does look exactly like what could be achieved from tape based archives today.

One can also replicate base Data Domain or Archiver appliances to an Archiver unit to achieve offsite data archives.

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Full disclosure: I currently work with EMC on projects specific to other products but am not currently working on anything associated with this product.

Tape, your move…

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Post tags: Archive, backup data retention, Data archive, Data Domain, Data Domain 860 Archiver, DD Boost, EMC, file backup data, Long term archive

Aurora's Perception or I Schrive When I See Technology by Wonderlane (cc) (from Flickr)

Some of these technologies were in development prior to 2000, some were available in other domains but not in storage, and some were in a few subsystems but had yet to become popular as they are today.  In no particular order here are my top 10 storage technologies for the decade:

1. NAND based SSDs - DRAM and other technology solid state drives (SSDs) were available last century but over the last decade NAND Flash based devices have dominated SSD technology and have altered the storage industry forever more.  Today, it’s nigh impossible to find enterprise class storage that doesn’t support NAND SSDs.
2. GMR head - Giant Magneto Resistance disk heads have become common place over the last decade and have allowed disk drive manufacturers to double data density every 18-24 months.  Now GMR heads are starting to transition over to tape storage and will enable that technology to increase data density dramatically
3. Data Deduplication – Deduplication technologies emerged over the last decade as a complement to higher density disk drives as a means to more efficiently backup data.  Deduplication technology can be found in many different forms today, ranging from file and block storage systems, backup storage systems, to backup software only solutions.
4. Thin provisioning – No one would argue that thin provisioning emerged last century but it took the last decade to really find its place in the storage pantheon.  One almost cannot find a data center class storage device that does not support thin provisioning today.
5. Scale-out storage – Last century if you wanted to get higher IOPS from a storage subsystem you could add cache or disk drives but at some point you hit a subsystem performance wall.  With scale-out storage, one can now add more processing elements to a storage system cluster without having to replace the controller to obtain more IO processing power.  The link reference talks about the use of commodity hardware to provide added performance but scale-out storage can also be done with non-commodity hardware (see Hitachi’s VSP vs. VMAX).
6. Storage virtualization – server virtualization has taken off as the dominant data center paradigm over the last decade but a counterpart to this in storage has also become more viable as well.  Storage virtualization was originally used to migrate data from old subsystems to new storage but today can be used to manage and migrate data over PBs of physical storage dynamically optimizing data placement for cost and/or performance.
7. LTO tape - When IBM dominated IT in the mid to late last century, the tape format dejour always matched IBM’s tape technology.  As the decade dawned, IBM was no longer the dominant player and tape technology was starting to diverge into a babble of differing formats.  As a result, IBM, Quantum, and HP put their technology together and created a standard tape format, called LTO, which has become the new dominant tape format for the data center.
8. Cloud storage - Unclear just when over the last decade cloud storage emerged but it seemed to be a supplement to cloud computing that also appeared this past decade.  Storage service providers had existed earlier but due to bandwidth limitations and storage costs didn’t survive the dotcom bubble. But over this past decade both bandwidth and storage costs have come down considerably and cloud storage has now become a viable technological solution to many data center issues.
9. iSCSI - SCSI has taken on many forms over the last couple of decades but iSCSI has the altered the dominant block storage paradigm from a single, pure FC based SAN to a plurality of technologies.  Nowadays, SMB shops can have block storage without the cost and complexity of FC SANs over the LAN networking technology they already use.
10. FCoE – One could argue that this technology is still maturing today but once again SCSI has taken opened up another way to access storage. FCoE has the potential to offer all the robustness and performance of FC SANs over data center Ethernet hardware simplifying and unifying data center networking onto one technology.

No doubt others would differ on their top 10 storage technologies over the last decade but I strived to find technologies that significantly changed data storage that existed in 2000 vs. today.  These 10 seemed to me to fit the bill better than most.

Comments?

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Post tags: Cloud Storage, Deduplication, FCoE, GMR head, iSCSI, LTO tape, NAND, Scale-out storage, SSD, Storage virtualization, Thin provisioning

Isilon X series nodes (c) 2010 Isilon from Isilon's website

I understand the rationale behind EMC’s purchase of Isilon scale out NAS technology for big data applications.  More and more data is being created every day and most of that unstructured.  How can one begin to support multiple PBs of file data that’s coming online in the next couple of years without scale out NAS.  Scale out NAS has the advantage that within the same architecture one can scale from TBs to PBs of file storage by just adding storage and/or accessor nodes.  Sounds great.

Isilon for backup storage?

But what’s surprising to me is the use of Isilon NL-Series storage in more mundane applications like Database backup.  A couple of weeks ago I wrote a post on how Oracle RMAN compressed backups don’t dedupe very well.  The impetus for that post was that a very large enterprise customer I was talking with had just started deploying Isilon NAS systems in their backup environment to handle non-dedupable data.  The customer was backing up PB of storage, a good portion of which was non-dedupable, and as such, they planed to use Isilon Systems to store this data.

I had never seen scale out NAS systems used for backup storage so I was intrigued to find out why.  Essentially, this customer was in the throws of replacing tape and between deduplication appliances and Isilon storage they believed they had the solutions to eliminate tape forever from their backup systems.

All this begs the question where does EMC put Isilon –  with Celerra and other storage platforms, with Atmos and other cloud services, or with Data Domain and other backup systems?  It seems one could almost break out the three Isilon storage systems and split them into these three business groups but given Isilon’s flexibility it probably belongs in storage platforms.

However, I would think that BRS would have an immediate market requirement for Isilon’s NL-Series storage to complement it’s other backup systems.  I guess we will know shortly where EMC puts it – until then it’s anyone’s guess.

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Post tags: backup systems, EMC, Isilon Systems, Scale out NAS, SO/CFS, tape elimination

Free Whipped Cream Clouds on True Blue Sky Creative Commons by Pink Sherbet Photography (cc) (from Flickr)

I was talking with another cloud storage gateway provider today and I asked them if they do any sort of backup for data sent to the cloud.  His answer disturbed me – they said they depend on backend cloud storage providers replication services to provide data protection – sigh. Curtis and I have written about this before (see my Does Cloud Storage need Backup? post and Replication is not backup by W. Curtis Preston).

Cloud replication is not backup

Replication does a nice job of covering a data center or hardware failure which leaves data at one site inaccessible but allows access to a replica of the data from another site.  As far as I am concerned there’s nothing better than replication for these sorts of DR purposes but it does nothing for someone deleting the wrong file. (I one time did a “rm * *” command on a shared Unix directory – it wasn’t pretty).

Some cloud storage (backend) vendors delay the deletion of blobs/containers until sometime later  as one solution to this problem.  By doing this, the data “stays around” for “sometime” after being deleted and can be restored via special request to the cloud storage vendor. The only problem with this is that “sometime” is an ill-defined, nebulous concept which is not guaranteed/specified in any way.  Also, depending on the “fullness” of the cloud storage, this time frame may be much shorter or longer.  End-user data protection cannot depend on such a wishy-washy arrangement.

Other solutions to data protection for cloud storage

One way is to have a local backup of any data located in cloud storage.  But this kind of defeats the purpose of cloud storage and has the cloud data being stored both locally (as backups) and remotely.  I suppose the backup data could be sent to another cloud storage provider but someone/somewhere would need to support some sort of versioning to be able to keep multiple iterations of the data around, e.g., 90 days worth of backups.  Sounds like a backup package front-ending cloud storage to me…

Another approach is to have the gateway provider supply some sort of backup internally using the very same cloud storage to hold various versions of data.  As long as the user can specify how many days or versions of backups can be held this works great, as cloud replication supports availability in the face of hardware failures and multiple versions support availability in the face of finger checks/logical corruptions.

This problem can be solved in many ways, but just using cloud replication is not one of them.

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Listen up folks, whenever you think about putting data in the cloud, you need to ask about backups among other things.  If they say we only offer data replication provided by the cloud storage backend – go somewhere else. Trust me, there are solutions out there that really backup cloud data.

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Post tags: Cloud gateway, Cloud storage backup, Cloud storage gateways

Oracle offices by Steve Parker (cc) (from Flickr)

I was talking with one large enterprise customer today and he was lamenting how poorly Oracle RMAN compressed backupsets dedupe. Apparently, non-compressed RMAN backup sets generate anywhere from 20 to 40:1 deduplication ratios but when they use RMAN backupset compression, their deduplication ratios drop down to 2:1.  Given that RMAN compression probably only adds another 2:1 compression ratio then the overall data reduction becomes something ~4:1.

RMAN compression

It turns out Oracle RMAN supports two different compression algorithms that can be used zlib (or gzip) and bzip2.  I assume the default is zlib and if you want to one can specify bzip2 for even higher compression rates with the commensurate slower or more processor intensive compression activity.

• Zlib is pretty standard repeating strings elimination followed by Huffman coding which uses shorter bit strings to represent more frequent characters and longer bit strings to represent less frequent characters.
• Bzip2 also uses Huffman coding but only after a number of other transforms such as run length encoding (changing duplicated characters to a count:character sequence), Burrows–Wheeler transform (changes data stream so that repeating characters come together), move-to-front transform (changes data stream so that all repeating character strings are moved to the front), another run length encoding step, huffman encoding, followed by another couple of steps to decrease the data length even more…

The net of all this is that a block of data that is bzip2 encoded may look significantly different if even one character is changed.  Similarly, even zlib compressed data will look different with a single character insertion, but perhaps not as much.  This will depend on the character and where it’s inserted but even if the new character doesn’t change the huffman encoding tree, adding a few bits to a data stream will necessarily alter its byte groupings significantly downstream from that insertion. (See huffman coding to learn more).

Deduplicating RMAN compressed backupsets

Sub-block level deduplication often depends on seeing the same sequence of data that may be skewed or shifted by one to N bytes between two data blocks.  But as discussed above, with bzip2 or zlib (or any huffman encoded) compression algorithm the sequence of bytes looks distinctly different downstream from any character insertion.

One way to obtain decent deduplication rates from RMAN compressed backupsets would be to decompress the data at the dedupe appliance and then run the deduplication algorithm on it – dedupe appliance ingestion rates would suffer accordingly.  Another approach is to not use RMAN compressed backupsets but the advantages of compression are very appealing such as less network bandwidth, faster backups (because they are not transferring as much data), and quicker restores.

Oracle RMAN OST

On the other hand, what might work is some form of Data Domain OST/Boost like support from Oracle RMAN which would partially deduplicate the data at the RMAN server and then send the deduplicated stream to the dedupe appliance.  This would provide less network bandwidth and faster backups but may not do anything for restores.  Perhaps a tradeoff worth investigating.

As for the likelihood that Oracle would make such services available to deduplicatione vendors, I would have said this was unlikely but ultimately the customers have a say here.   It’s unclear why Symantec created OST but it turned out to be a money maker for them and something similar could be supported by Oracle.  Once an Oracle RMAN OST-like capability was in place, it shouldn’t take much to provide Boost functionality on top of it.  (Although EMC Data Domain is the only dedupe vendor that has Boost yet for OST or their own Networker Boost version.)

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When I first started this post I thought that if the dedupe vendors just understood the format of the RMAN compressed backupsets they would be able to have the same dedupe ratios as seen for normal RMAN backupsets.  As I investigated the compression algorithms being used I became convinced that it’s a computationally “hard” problem to extract duplicate data from RMAN compressed backupsets and ultimately would probably not be worth it.

So, if you use RMAN backupset compression, probably ought to avoid deduplicating this data for now.

Anything I missed here?

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Post tags: bzip2, Deduplication, huffman coding, Oracle, Oracle RMAN, RMAN backupsets compression, Symantec OST, zlib