What is Virtual Tape Library

[Varma_Chiluvuri]

Can someone please explain What is Virtual Tape Library (VTL) in Symantec Netbackup, how is it useful?

[MKT]

Hopefully this helps:

http://eval.symantec.com/mktginfo/enterprise/white_papers/b-whitepaper_using_virtual_tape_libraries_...

[mph999]

A VTL is a disk device with a controller, which NBU thinks is a real library.

Personally, I'm not a fan, though the abilty to have the performance of disk, but look  like tapes keeps things easy to understand.  They are particularly good if your clients can only produce low throughput of data, as they do not suffer from 'shoe-shining' which damages real drives and tapes when they are run too slowly.

You can then duplicate the images to tape, this will usually run the real drives at a good speed, as you are coming from dedicated disk.

However, you can achieve this just using a basic disk/ advanced disk storage units (but they don't look like tapes).

Personally, I have seen more data lost (and I mean really lost) through problems with VTLs than with any other cause, that is, the 'fault' of the VTL not NetBackup).

I will take this oppotuninty to add ...

Backups should never only be run to disk, even if the disk (or VTL) replicates itself to another disk (or VTL) device outside of NetBackup - this does not prevent against corruption  - if the disk is corrupted, this could be copied across and you could lose everything.  If you duplicate to tape, then only a small amount of data might be lost, as the tapes are separate.

Yes, I have seen this, and it's not pretty ...

Martin

[Varma_Chiluvuri]

Thanks Martin and MKT.

Martin, Where does VTL stores the data. If it stores to a disk or tape, then what is the use of VTL?

[Yogesh9881]

Where does VTL stores the data------>VTL stores data actually in to disk (it look like a tape).

what is the use of VTL?-------> Totally Depends on your business need

[falti_manullang]

A virtual tape library (VTL) is physically a highly intelligent optimized disk-based storage appliance. Because a VTL completely emulates a standard library, the introduction of virtual tape is seamless and transparent to existing tape backup/recovery applications.

A virtual tape library solution can perform 10-times tape speeds for backups. Speeding up the backups will greatly shrink the backup window, which allows servers to be backed up faster. With existing backups finishing quicker, second- and third-tier servers that have not been backed up in the past may now fit into the backup schedule.

Recoveries are also significantly faster using a VTL (typically much faster than the backup). A single file can be recovered from a VTL faster than most tape libraries can find and load a tape into a drive. Full backups that span multiple tapes (as apposed to multiplexed) will also recover very slowly compared to a VTL since after the data is read from one tape the next tape must be located and loaded compared to a VTL that just keeps streaming data from disk.

All virtual tape loads are immediate so there is virtually no delay when a new "tape" is "loaded." People who resort to multiplexing backups to increase the performance of the backup are usually shocked to discover that their recovery times will be about twice as long as the backup was.

Most virtual tape library solutions also contain RAID-protected storage that has redundant, hot-swap components (drives, power, cooling). Backups that use a VTL rarely fail because of a VTL failure. Recoveries will never fail due to a bad or lost tape.

VTLs are just not prone to the types of failures that a traditional tape library has. For example, a backup to disk will never fail because of a bad tape, broken tape drive or broken robotics.

:)

[mph999]

As mentioned by falti , a VTL stores data on disk.

A VTL is simply a disk drive, that via software  or hardware, is made to look like a real library.

The concept, is as simple as that.

Once the data is on the VTL, some customers use NetBackup to duplicate the images to real tapes.  Some VTLs are more clever, and can attach to their own tape drives, and archive the data off without NBU.  

"A virtual tape library solution can perform 10-times tape speeds for backups" ...

I would not say this is true all the time ...  Tape drives today can be as fast as disk, if not , faster.  Probably the most common factor that makes backups 'slow' is because the clients cannot get the data to the tape drives quickly enough (eg, the network is the slow point), a VTL does not fix this, and will not run any quicker.  What it will do, is avoid show-shining the drives though, which is a big advantage, but this can also be done with basic disk storage units which are cheaper.

I agree that a VTL should retsore a few files quicker than tape, but then again, so will a disk storage unit.

"Backups that use a VTL rarely fail because of a VTL failure. " - Oh yes they do ....  Disks can and do fail, hardware in general can fail.

Personally my view is that  tape drives that are correctly implemented into a backup environment, that are correctly looked after with tapes that are correctly looked after, are reliable.  The problem with real tape dries, is that they have to be run a bove a certain speed to stream, and on average, many people do not do this.  LTO drives are common,  and have to stream else they stop/start which wreaks them, and the tapes.  However, certain other drives (eg STK drives) are designed to stop/start and have no such limitations - so , desiginging a backup environment is about using the right type of drives, and many people use LTO drives when hen are unsuitable, due to the limitations of the speed they can get the data off the clients.

"VTLs are just not prone to the types of failures that a traditional tape library has. For example, a backup to disk will never fail because of a bad tape, broken tape drive or broken robotics."

- Yes, agree with that, but tape failure as explained above can be minimised by proper managment and care.  however, VTLs can corrupt, and you risk losing everything.  Hence why on my previous post, backups should never never only go to disk, even if that disk is replicated.

Martin

[falti_manullang]

Disk just for staging, after that duplicate to tape with Storage Lifecycle Policy (SLP).

[mph999]

yeah

Disk just for staging, after that duplicate to tape with Storage Lifecycle Policy (SLP).

Yep, spot on ....   or , just use Basic disk staging ....

Or if youare feeling 'flash' you could use the post-backup scripts to kick off your duplicates to tape ....

Martin

[Varma_Chiluvuri]

1) Once VTL stores data in to disk, will the data be copied to Tape after sometime?

2) Can we configure VTL on Tapes also?

3) The only advantage of VTL is the data backup will be fast. Am I right?.

4) If VTL Stores data into physical disk, then why it is called virtual Tape Library?.

[Yogesh9881]

please read carefully .....

http://eval.symantec.com/mktginfo/enterprise/white_papers/b-whitepaper_using_virtual_tape_libraries_...

[Deepak_G · Accepted solution]

Pls find the answers

1) Once VTL stores data in to disk, will the data be copied to Tape after sometime?

It can be configured to be moved to tape or if needed we can store is based on our retention policy. So some critical apps with smaller retention periods its better to store in VTL as backup and recovered are faster. VAULTING and STORAGE LIFECYCLE POLICIES are used in netbackup to automate that process.

2) Can we configure VTL on Tapes also?

No - Virutal tapes can be configured on disks only. You need to understand that a tape again cannot be used as virtual tape.

3) The only advantage of VTL is the data backup will be fast. Am I right?.

There are other advantages too.

• Storage consolidation
• Faster backup and restore process
• Problems in tape drives reduced increasing the efficiency of the drives
• Disk to Disk backups and then the copy is duplicated seperately from Disk to tapes in vaulting.

4) If VTL Stores data into physical disk, then why it is called virtual Tape Library?. 

Because for netbackup we dont show it as disk but we have tape enumerator software (Resident softwares) which converts and show the blocks of disks as tapes.

We use netbackup to configure backup on seperate set of tapes. In the same ways in a disk of 1 TB size, we create partitions of 100 GB each. So each of these partitions are named as VTL tapes and presented to netbackup. Its a physical disk but a virutal tape.

You can go through all these above comments. That gives you a clear picuture of what a virutal tape library is. Since its virutal and not available physical these physical disks are named as virutal tape libraries. (Just like the virutal machines - they are not physical machines)

[Varma_Chiluvuri]

Thank you very much everyone for giving me a clear understanding about VTL, I am just starter to Netbackup, hope this will be a good start to me :)