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Virtual librarys, software or hardware ?

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Leif Halvarsson_2
Honored Contributor

Virtual librarys, software or hardware ?


Since some time, there has been hardware virtual librarys (disk systems which emulates a tape library) on the market, also HP has launched a such device:

But, today most backup applications has the same (or similar) concept implemented in software (e.g. Data Protector Advanced Backup to Disk).

Is there actualy any advantages with a hardware virtual library (compared to a software ). And, is there any market for them ? Anyone who has any experience ?

And, anyone who has any comments ?
Richard Rydström
Valued Contributor

Re: Virtual librarys, software or hardware ?

Hi Leif

There could be an advantage with licensing. You can re-use your old tape library license for your backup application instead.
Also, with normal backup-2-disk you have to allocate LUNs/diskspace to a specific server. Meaning that if you assign 1 TB to serverA, serverB needs own dedicated disk space for backup to disk =disk space cannot be shared between hosts.

With VirtualLibarySystem each tape drive and "disk space" (virtual medias) are shared between all hosts you wish.=better utilization

Honored Contributor

Re: Virtual librarys, software or hardware ?

Hi Leif,

Hope you will find your answer here.

Uwe Zessin
Honored Contributor

Re: Virtual librarys, software or hardware ?

Another thing is if the tape drive is 'too fast' for the server. A virtual tape library doesn't do 'shoe-shining'.
Marino Meloni_1
Honored Contributor

Re: Virtual librarys, software or hardware ?

My opinion is that using the VLS is better for the following reasons:

-Installation is already done, just attach the unit and configure the emulation and tapes.
In the backup to disk, you need to configure your array, or collect space on it, and share it with the other data.

- You have a dedicated hardware VS a shared one.

- You can manage it with CommandView TL as a library

- You can use it as a real tape library, if your server is down, just attach it to another server, and import the tape with the database, you will have your virtual cartridges ready early

- If you need Disk to Disk to Tape, using the serverless function will reduce the server activity, as the data will flow directly from the VLS to the Library

- and finaly, when do you need to restore from tape? When your disk system crash, so better to have backup in a separate entity

Stuart Whitby
Trusted Contributor

Re: Virtual librarys, software or hardware ?

Leif asks questions?!? I thought you knew everything? ;)

If the virtual tape emulation software is good, then I think this is a great idea. Backup to disk is still relatively immature technology, so having a disk that emulates tape is excellent.

Disk is more reliable (under RAID) in that you're no longer having to perform that recover of your payroll database and *just hoping* that you don't hit a bad block on tape. They're very rare on disk, but not so rare on tape. It's also a whole lot cheaper to have a bunch of drives set up on here than it is to pay for similar quantities of tape drive hardware.

The only other real advantage that I see is that there's no maximum capacity on these drives. With NetWorker, if you set up backup to disk, you'll also specify a maximum size for each disk partition. You can stream to these "tape" drives until the entire library hits capacity though.

Otherwise, there's not a lot of reason to choose a virtual library over a large disk array. Give it another couple of years and backup to disk will probably be on a par with backup to tape, but until then I figure this is a better option.

You're still going to need tape for archive and offsite purposes, btw.
A sysadmin should never cross his fingers in the hope commands will work. Makes for a lot of mistakes while typing.
Mats Holm_1
Valued Contributor

Re: Virtual librarys, software or hardware ?

Hi Leif!

A lot of good reasons to chosse vitual arrays but haven't seen the biggest advantage against "normal" backup-to-disk as I see it. That is that you'll have harware compression. If you buy one with 5GB disk you're able to store 10GB of backup data and for the prize of a 5TB DP Advanced-to-disk license!!!

Jason Wildt
Occasional Visitor

Re: Virtual librarys, software or hardware ?

The primary benefits of Virtual Tape over Disk as a target can be broken into 3 categories: Manageability, Performance, and Storage Efficiency.

Installation - the virtual tape library is accepted by the existing application as a new library, no RAID sets, LUNs, Volumes or File Systems to configure and provision.
Ongoing maintainance - Array management (how full is the LUN, is it fragmented, etc.) are all managed and executed on by the virtual tape device, offloading these tasks from storage administrators.
The level of manageabilty varies by vendor - what is described here is based on the HP solution

A typical disk array is tuned for I/O performance, not streaming performance. In a virtual tape library, the RAID, LUN and Filesystem configurations are tuned for the sequential throughput required by backup and recovery applications.

Storage Efficiency:
The virtual tape library can perform device-side compression allowing similar data compression to LTO tape drives. Unlike tape, in most currently shipping virtual libraries (HP model included) the compression is software enabled thus performance is degraded when it is used.

Does this mean there is not a place for disk as a backup target? The answer to that is no.

It really comes down to the economics of dealing with the complexity vs. the cost of implementation. Generally smaller installations will benefit from disk as target.
For example, if there are relatively few (maybe 5 or fewer) servers and the management overhead of the array is not significant. In those same small environments, there may be ample performance to achieve the backup windows. And finally, if you already have the extra storage, maybe compression is not a big deal.
Leif Halvarsson_2
Honored Contributor

Re: Virtual librarys, software or hardware ?


Thanks to all of you for your input. I have made a short summary (and some comments).

- Licensing may be a reason if you don't need to migrate data from disk to tape.
- Data compression. Perhaps the best argument.
- Performance. Hardware virtual librarys are optimized for throughput rather then IOPS. But, I doubt if it will make much difference in the real world. In most cases, the bottleneck is with the data you want to backup, not where you write the data.

- Management. I have not enough experience to make a comparision myself.

I have found a few additional reasons.

- The backup software don't support or have a poor implementation of disk backup (as previous versions of OB/DP)
- Media copy. Data can be migrated to tape, media for media. With software virtual librarys, data must be migrated as objects.

David Ruska
Honored Contributor

Re: Virtual librarys, software or hardware ?

Note: This thread was moved from "tape library and drives".
The journey IS the reward.
Respected Contributor

Re: Virtual librarys, software or hardware ?

Hi Leif,

as I mentioned in anothere thread ( -> )
Dataprotectors Software Solution "Advanced Backup to Disk" is benefitial for LAN Hosts only (!) and Virtual Tape Library Hardware Appliances are great solutions for SAN Hosts.
These are the key factors that I've learned for myself during the presentation of HP's new Virtual Tape Library Systems at ENSA 2005.

I thought it's worth adding this additional info to your original thread.

Leif Halvarsson_2
Honored Contributor

Re: Virtual librarys, software or hardware ?


As Software Virtual librarys is emulated on a client, the data flow must go via LAN. It is very obvious but, easy to forgot before you have configured a such device yourself.

Thank you.

Regular Advisor

Re: Virtual librarys, software or hardware ?

I would like to add another argument.

Traditional backup to disk is vulnerable for virus attacts. The "VLS" like systems are much more likly to be affected by this threat.

And offcours "Advanced Backup To Disk" as deliverede from HP and other are mainly a disk resource owned by a singel host.

Kurt Beyers.
Honored Contributor

Re: Virtual librarys, software or hardware ?


There is a white paper called 'The role of HP StorageWorks 6000 Virtual Library Systems in a modern data protection strategy white paper' at

A comparison with disk and tape based backups is made too.