Straight Disk or VTL for TSM Storage Pool

[Wfitzgerald]

My company is in the process of determining how or what to do to eventually remove all tape based primary storage for our mission critical systems.

The scenario is that the primary backup will go to disk and the secondary will go to tape. The Disk will be on LTO4 tape.

The issue at hand is should be disk based system be a straight disk or a VTL of some flavor.

I am looking for input from administrators that have used either straight disk or VTL. What are the advantages and disadvantages of each ? I am worried about data fragmentation adn lack of reclamation on straight disk space.

Some of our mission critical systems have large turn over in the data, like the 5.0 tb oracle database. others run on Microsoft cluster with huge numbers of files but only a small percent turnover on a weekly basic.

Any help, advice, information you can give me or point me to would be of great help.

William Fitzgerald
TSM administrator
Bridgehead Administrator
Munson Medical Center

 

[Raakin]

This has been beat over a couple of times. Some points that have stood out to me are the following:

1. VTL is Disk - So basic but so important!
2. Realize what the VTL solution will give you that plain disk won't and see if the cost difference or business need justifies the VTL.
3. VTL could be considered a reserved section of disk.
4. VTL emulates tapes so all procedures to interact with it will be 'tape procedures'.
5. Key 'selling' feature is dedup. Realize as dedup/compression are introduced so is risk. Be sure how the VTL midigates that risk.
   1. Is TSM 6.1 dedup sufficent?
6. Look at the type of data you plan to use the VTL/Disk for. Databases do not dedup well and may not be worth the 'VTL' price.
7. http://www.adsm.org/forum/showthread.php?t=12569
8. http://www.adsm.org/forum/showthread.php?t=15192
9. http://www.adsm.org/forum/showthread.php?t=13449
10. http://www.google.com/custom?sitesearch=adsm.org/forum and put in your "disk vs VTL" search terms, very helpful to answer specific questions you may have.

 

[DanGiles]

What you do will really depend on RTO, RPO, recovery procedures, and the like. For instance, if an application's data is being mirrored to a remote location, you don't need backup for DR purposes, so tape backups are fine.

So, for data that has an RTO that doesn't justify synchronous mirroring, but has to be faster than traditional tape, I would look at VTL. This VTL should have remote mirroring capabilities. If you are on, or planning to go on, TSM V6.x, then you can use the native dedupe and (a)synchronously mirror that particular file system remotely.

If you are not mirroring remotely, then my take is that, in a TSM environment, VTLs do not make sense. (Think about it - TSM has always acted like a VTL!)

P.S. after I posted I saw Raakin's comments. Not sure what he meant by "6.", but database backups compress extremely well. The compression ration you can expect is

1: (# of full db backups kept)

 

[zatogo]

I've argued this with our storage team a number of times...they said VTL wass the way to go...I said that since TSM has the intelligence built in that allows you to use "dumb disk" and avoid the additional cost of VTL go with the cheaper solution.

The one arguement I could not counter was their stance that you need VTL if you want to do LANFree to the diskpool. This makes sense since the LANFree agent needs tape drives (be they physical or virtual) to write to.


That being said...typically what goes LANFree is the big databases which don't gain the significant advantage of sitting on disk for faster recovery that a file server would...so you might as well put the big DB's to tape and save the cost of disk.

 

[THE_WIPET]

There is a simialr tread that was started a while back... "VTL vs Disk"
http://adsm.org/forum/showthread.php?p=68306#post68306

 

[srikumar_1]

My company is in the process of determining how or what to do to eventually remove all tape based primary storage for our mission critical systems.

The scenario is that the primary backup will go to disk and the secondary will go to tape. The Disk will be on LTO4 tape.

The issue at hand is should be disk based system be a straight disk or a VTL of some flavor.

I am looking for input from administrators that have used either straight disk or VTL. What are the advantages and disadvantages of each ? I am worried about data fragmentation adn lack of reclamation on straight disk space.

Some of our mission critical systems have large turn over in the data, like the 5.0 tb oracle database. others run on Microsoft cluster with huge numbers of files but only a small percent turnover on a weekly basic.

Any help, advice, information you can give me or point me to would be of great help.

William Fitzgerald
TSM administrator
Bridgehead Administrator
Munson Medical Center

I am not a big fan of disk storage and we use it for staging & active versions. As you said, If you have mission critical data...must go to tape (in this case VTL). We use VTL for primary and planning to have copypool VTL soon.
Disk will always have fragmentation issues and each file is stored in objects and will not hav good throughput for large sized files. Also depends on your operating systems disk will always have corruption issues unlike tape.
VTL with LT04 emulation works great for us

 

[blagrange]

The Benefits I can think of are:

1.) For primary or Active storage pools reclamations and data movement activities could be a smaller part of the daily processes (especially those who are limited on tape resources.)

2.) What is the cost per a TB on VTL opposed to SAN disk (including Dedupe etc.)?

On the other hand with TSM it is not a necessity to own a VTL. I look at it as a luxury. I think when looking at a solution you need to base it on your environment and really think of what problem does it solve for you.

If you cannot think of anything then you probably do not need it.