ATA vs. VTL, is there a right or wrong answer?

For years customer have been facing problems with backup windows, Recovery Point Objectives (RPO) and Recovery Time Objectives (RTO). The falling cost cost of storage has fueled the use of disk to increase the speed of backups and provide a potential solution to backup window, RPO and RTO issues. Customer today are leveraging the disk based backup solutions to augment their existing tape solutions in an effort to decrease backup time and recovery time as well as prolong investments in aging tape technology. Disk based backup solutions have taken numerous forms, leveraging ATA or LC-FC (low cost fibre channel) is a popular low cost solution that can normally be implemented in conjunction with an enterprise storage consolidation or integrated into an existing storage strategy.

The use of ATA or LC-FC can be a very economical introduction into the world of B2D. Often larger organizations shy away from traditional backup to disk because of the associated process change required and the potential increase in operational complexity. Organizations looking to benefit from the speed of disk without the need for process change may consider a VTL (virtual tape library) strategy. Virtual Tape also offers operational simplicity, in many cased native IP based replication, compression and/or data de-duplication. VTL devices are purpose built and optimized for backup this makes VTL a compelling choice. The caveat with VTL devices is that the simplicity of an emulated tape device also offers the many of the limitations and licensing costs associated with physical tape.

Organizations should also consider SLA requirements that typically encompass backup windows, RPO and RTO. What will the backup data flow be once a B2D solution is implemented? Will the architected B2D solution meet all the requirements of the SLA? In most cases the current state may look like D2T (production disk to tape), D2T2T (production disk to onsite tape copy to offsite tape copy) or D2Clone/Snap2Tape (disk 2 array based clone/snap 2 tape). Once a B2D strategy is employed the flow may look like any one of the following D2D2T, D2VT2T, or D2Clone/Snap2D2T, etc… The point here is that there are more ways than ever to implement backup solutions today, the pros and cons of each solution should be considered relative to the desired and/or required SLA, RPO and RTO.

-RJB

2 thoughts on “ATA vs. VTL, is there a right or wrong answer?

  1. Clearly you have a hand on the dilema of VTL or B2D. I enjoyed meeting up with you on the net and will mark your site.

    Matt Keane

  2. I’m deathly bored by horrible presenters at vmworld riht now, using my ‘berry to write this, so excuse and typos.

    Having deployed what was, at the time, the largest VTL in the world, and subsequently numerous other VTL and ATA Solutions, I think I can offer a somewhat different perspective:

    It depends on the number of data movers you have and how much manual work you’re prepared to do. Oh, and speed.

    Licensing for VTL is now capacity-based for most packages (at least the famous/infamous/important ones like CommVault, Networker and NetBackup, not respectively).

    Also, I’d forget about using VTL features such as replication and using the VTL to write directly to tape (unless you’re retarded, insane or the backup software is running ON the VTL, as is the case now with EMC’s CDL). Just use the VTL like tape. I’ve been so vehement about this that even the very stubborn and opinionated Curtis Preston is now afraid to say otherwise with me in the room… (I shut him up REALLY effectively during one Veritas Vision session we were co-presenting a couple years ago. I like Curtis but he’s too far removed from the real world. Great presenter, though, and funny).

    Even dedup features are suspect in my opinion, since they rely on hashes and searches of databases of hashes, which progressively get slower the more you store in them. Most companies selling dedup (data domain, avamar, to name a couple major names) are sorta cagey when you confront them with questions such as “I have 5 servers with 50 million files each, how well will this thing work?”

    Answer is, it won’t, even for far fewer files. Just get some raw-based backup method that also indexes, such as Networker’s snapimage or NBU’s flashbackup.

    Dedup also fails with very large files such as database files.

    I can expand on any of the above comments if anyone cares. I can be reached at dk@MTI.com or dikrek@gmail.com.

    But back on the data movers (Media Agents, Storage Nodes, Media Servers):

    Whether you use VTL or ATA, you effectively need to divvy up the available space.

    With ATA, you either allocate a fixed amount of space to each data mover, or use a cluster filesystem (such as Adic’s Stornext) to allow all data movers to see the same disk.

    With VTL, the smallest quantum of space you can allocate to a data mover is, simply, a virtual tape. A virtual tape, just like a real tape, gets automatically alocated, as needed.

    So, imagine you have a large datacenter, with maybe 40 data movers and multiple backup masters.

    Imagine you have a 64TB ATA array.

    You can either:

    1. Split the array into 40 chunks, and have a management nightmare
    2. Deploy stornext so all servers see a SINGLE 64TB filesystem (at an extra 3-4K per server, plus probably 50K more for maintenance, central servers and failover) – easy to deal with but complex to deploy and more software on your boxes)
    3. Deploy VTL and be done with it.

    For such a large environment, option #3 is the best choice, hands down.

    With filesystems, you have to worry about space, fragmentation, mount options, filesystem creation-time tunables, runtime tunables, esoteric kernel tunings, fancy disk layouts, and so on. If you’re weird like me and thoroughly enjoy such things, then go for it. As time goes by though, the novelty factor diminishes greatly. Been there, done that, smashed some speed records on the way.

    What’s needed in the larger shops, aside from performance, is scalability, ease of use and deployment, and simplicity.

    With VTL, you get all of that.

    The other issue with disk is that backup vendors, while they’re getting better, impose restrictions on the # streams in/out, copy to tape and so on. No such restrictions on tape.

    One issue with VTL: depending on your backup software, setting up all those new virtual drives etc. can be a pain (esp. on NBU).

    for a small shop (less than 2 data movers), a VTL is probably overkill.

    D

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