VTL vs. Disk Storage - Which one to go with? 1

[dukbtr]

Can anybody using these resources help?

We are budgeting for next years upgrade and we have to decide if we want to go with a VTL or just raw disk for D2D(2T). What are the advantages/disadvantages to either or both.

Some that we already know of is that Disk Storage requires managment of the disk space. VTL offers compression as a tape would. Other comments and answers would be greatly appreciated.

Thanks in advance,
Dukbtr

 

[Stumpr]

Three options:
1. Back up to a disk storage unit (DSU).
2. Back up to a disk staging storage unit (DSSU). This treats the disk like a big cache before the files get optionally written to tape
3. Back up to a virtual tape library (VTL). A disk looks like a tape drive to NetBackup.

DSU:
1. writes backup images to disk and the admin uses scripts to duplicate to tape.
DataDomain appliance (info from a user) DSU:
1. very little change to configuration/infrastructure.
2. Minor NBU changes.
3. 12:1 compression; gets better with longer retention period. 25TB of backup data on a 4TB physical disk array (DD460) and it’s only taking up 2.6TB
4. fantastic services/support. Emails sent home daily with performance stats. If they find anything not up to par they call you. The reports are saved on their website providing charted trend/forecast reports.
5. This customer duplicates the data to LTO2 tape and vaults them to offsite for DR.
6. Restores took 1 ½ hours rather than 2 hours to get the tapes and 6-8 hours to restore.

Pathlight:
1. maintains 1:1 relationship (virtual to physical tape) as opposed to VTL requiring that tapes first get re-imported before the restore. Also DR site requires the same VTL.
2. 1:1 relationship requires more storage.
3. turn-key
4. When it hits 85% full it offloads data. Throughput is only 1T/hr while others are pushing 2T/hr or more.

DSSU:
1. Set duplication”frequency”, error_behavior, and multiple copies.
2. if the DSSU fills up backups fail.
3. success is dependent on the disk-write speeds being comparable to the disk-read speeds. One user set up two DSUs and alternated daily between them, having to modify policies every day.
4. DSSUs are locked to the host they are on. This may be fixed in NBU V6 where jobs are allowed to write to multiple DSSUs I think.

VTL:
1. Aren’t subject to filesystem size limitations that several OS’s have.
2. VTLs are more portable than DSSUs. Any system on the fabric can access a backup written by a TLD. DSSUs are locked to the host they are on. May be fixed in NBU v6
3. Two users don’t see VTL as a long term solution. Will be killed off by DSU.
4. Designed to improve tape utilization. Tapes are written when there is enough data to fill a tape. The VTL isn’t maintaining any correspondence with the backup software. Most tapes will be full but this doesn’t accommodate daily offsite requirement.
5. VTL requiring that tapes first get re-imported before the restore.
6. DR site requires the same VTL.
7. Quantum DX series had hardware compression (rare for a VTL).
8. VTL manages the disk subsystem capacity not NBU.


Bob Stump
Just because the VERITAS documentation states a certain thing does not make it a fact and that is truth.