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VLS Virtual Tape Libary Vs. Disk based backups

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Amy Bach_1

VLS Virtual Tape Libary Vs. Disk based backups

Hi all,

We are looking to implement a disk-to-disk-to-tape (D2D2T)backup solution, we are however not sure how to approach this. Before the introduction of VLS systems, the choice was simple, get some cheap storage (ATA, SATA, or FATA Drives), create LUNS to be used for backup, configure disk backup, set up copy job to copy from disk to tape. Now, with the introduction of VLS, we are not sure if this is the best way to do it. We care currently deciding between and MSA1500 with SATA drives, or a VLS9518 system.

I know the white papers give some reference as to when a VLS is better than traditional disk-disk backups, but the difference is not very clear. Perhaps it is not much a clarity issue as it is a pricing issue.

I can see the benefits of the VLS (you get the speed of disk backups, plus media managability of physical tapes), however, it is tough to justify the cost for the VTL.

In our environment we are running Netbackup 6.0, we have 30 clients that backup nightly (currently via gigabit LAN). Out of the 30 servers only 5 are critical servers and currently on the SAN. In Netbackup there is no additional cost associated with traditional disk-disk backups, however, there is a TB usage license for VTLs. On top of the TB usage license, SSO license is required to share virtual libraries (just as physical libraries do).

Can someone give some input on the pros/cons of both solutions? If you currently have a VLS in your data center how does it compare with traditional disk-to-disk backups? Is the performance/manageability difference so great to justify the added VLS costs?

Thanks for your help!




P.S. This thread has been moevd from Tape Backup (Small and Medium Business) to Disk-Based Backup. - Hp Forum moderator

Jason Wildt
New Member

Re: VLS Virtual Tape Libary Vs. Disk based backups

There are many differences between disk-as-target and virtual tape. We can talk about these in 3 main categories: Manageability, Performance, and Capacity.

The VLS6000 manages all of the array functions. With disk as target, you must manage creation of the RAID sets, creation of the LUNs, on-ongoing monitoring of the LUNs and defragmentation. In small installations where only one server may be accessing the disk, this could be manageable. As the number of servers increase, the management headache grows.

While disk as target does introduce disk into the backup process, it still typically uses a complex file system to store the backed up data. This reduces the performance of the process. The VLS system uses a specialized file system that distributes the data over all the LUNs. The result is performance that can be up to 10x greater than that of a standard SATA array. In your case you have spec'ed the VLS6518 with a maximum through put of 400 MB/s. I would expect to see 3x to 5x beter performance than a MSA1500. For you LAN servers, the virtual tape allows you to present enough resources that multiplexing is no longer necessary. This will improve the speed of restore regardless of the location (disk or tape). The final performance impact is on the copy to tape motion. With the virtual tape, your backup server can access all the media and perform transfers to tape. In most disk as target applications, the data path for movement to physical tape goes back through the server that owns the LUN (i.e. you affect the application server twice - once on the backup and once on the transfer to tape).
While I have not personally deployed a VLS in the data center, I have spoken to people who have that are seeing 2x-5x improvement in backup performance.

The Virtual Library System has onboard compression capabilities. These will give tape-like compression, however they do come at a cost. In the case of the 6518, I would expect to see up to 50% reduction in performance. This still provides more throughput than an MSA1500, but gives you more capacity.

To sum up Virtual Tape
* simplifies managment when there are multiple servers writing data
* Higher performance (both LAN and SAN backups)
* Compression is available


Just one other thing - with Symantec/Veritas NetBackup, you will most likely need the vaulting license to migrate from virtual tape to physical tape.
Hopefully this has helped.

Tim Medford
Valued Contributor

Re: VLS Virtual Tape Libary Vs. Disk based backups

Hi Amy.

We are facing a very similar choice in our data center. Just wondering which route you went and how things worked out?