I am deploying a NetApp VTL 1400 (VTL OS Version 6.0) at my local site.
I am working with the NetApp engineer assigned to our deployment to
layout which policies are written to which virtual library, etc. The
topic of Direct Tape Creation came up and I'm getting some information
that is greatly confusing me, and I wanted to blast a message out to the
board here to get some feedback.
First, an quick idea of my layout and assumptions that I'm making about
why we bought the VTL in the first place.
Assumptions: One of the principle reasons anyone deploys a VTL is because:
* Disk is faster than tape at the expense of
disk not being removeable and having a lower Mean Time Between Failures
than tape.
* Backup windows are shrinking. A VTL allows you
to create several "virtual drives" that allow you to write more backups
concurrently, thus shrinking your backup window.
Here's my current layout:
Hardware: Spectra Logic T380 with 12 IBM LTO4 tape drives.
* I'm told the theoretical bandwidth of an LTO4 tape
drive is approximately 120 MB/s. If I have 12 drives, I'm assuming I can
say that my library should theoretically be able to handle data at (12 x
120 MB/s) 1,440 MB/s. I currently have a performance bottleneck in that
I have a couple hundred clients that are backing up over the LAN. Any
one client writes at approximately 25 MB/s to 45 MB/s. So I have a
physical library that can receive data faster than my LAN can pump it.
I've addressed this with management and we're considering some
technologies to increase our client's ability to pump data faster to the
Spectra Logic library.
Policies: I have my policies staggered throughout the night. I have a
batch that kicks off at 6pm, another batch that kicks off at 8pm, 10pm,
Midnight and 2 am.
NetBackup: 1 Master (linux), 2 Media (linux), and 3 San Media Servers
(Tru64).
Here's the layout I have in my head for the VTL.
______________ _______
________ _________________
| NetBackup | -------> | SAN | ---------> | VTL | ------------> |
Spectra Logic |
------------------- -----------
----------- ------------------------
In other words, I want to zone the VTL so that it's the only "library"
seen by NetBackup, and then have my Spectra Logic zoned so that it's
"behind" my VTL. Furthermore, I've read Symantec's white paper on VTL's
and they recommend *NOT* using Shared Storage Option (SSO) with a VTL.
So I essentially want to make three virtual libraries, each with maybe
20 or 30 drives, and present each library to my Master and two Media
servers, like this:
Master Server ----> Virtual Library 1 (This library has 20 to 30 drives
and is zoned so that it is only seen by the Master Server).
Media Server 1 ----> Virtual Library 2 (This library has 20 to 30 drives
and is zoned so that it is only seen by the first Media Server).
Media Server 2 -----> Virtual Library 3 (This library has 20 to 30
drives and is zoned so that it is only seen by the second Media Server).
With the 60 to 90 drives that would provide, I could setup a storage
unit for each "library", and then each night just start ALL my policies
and 6 pm and each one would get a drive and begin writing. This
configuration would definitely shrink my backup window.
However ... (there's always a catch, isn't there?)
I want to use Direct Tape Creation so that when I come in in the
morning, I can write all of last night's backups out to physical media
to be taken offsite. My NetApp engineer tells me that when you enable
Direct Tape Creation on a Virtual Library, that the Virtual Library has
to have a 1-to-1 relationship with the physical library behind it.
In other words, since my physical library has 12 tape drives and 1
robot, my VTL is limited to having 12 tape drives and 1 robot. If that's
true, then I'm completely confused about what the point was in buying
the VTL. I thought I'd be able to:
* Setup the configuration I described previously.
* Set all my backup policies to kick off at 6 pm. With 60 to 90 virtual
drives available, most if not all of my clients would get a tape drive
to write to. The rest would queue up and wait for a resource. I say good
bye to status code 196.
* I come in in the morning, log into my VTL and kick off the operation
to write last night's backups from virtual tape to physical tape. My
Spectra Logic only has 12 physical drives, so the first 12 virtual tapes
that needed to be written to physical tape would get a physical drive to
write to, and the other 50+ tapes would just queue up on the VTL and
wait for a free LTO4 drive in the Spectra Logic to become available.
If what my NetApp engineer is telling me is correct, I'm only going to
be able to present a single virtual library, consisting of 12 virtual
drives, to NetBackup. So now I'm back to my original problem:
* I have a "library" that can receive data much faster than my network
can deliver it.
* Even if I was able to pump data at 100 MB/s - 150 MB/s, I'm now
limited to the fact that I can only be doing 12 backup restore
operations at a time.
* My backup window doesn't change at all. Sure I have shadow tapes and a
couple of neat features on the VTL. But the underlying premise, that the
VTL could shrink my backup window by allowing me to present tens if not
hundreds of virtual drives to my backup application and therefore run
all my policies concurrently, doesn't appear to exist.
Am I missing something? Is anyone else running a NetApp VTL and
utilizing Direct Tape Creation? If so, what does your environment and
configuration look like? If my engineer is correct and I can only
present a single library of 12 drives to NetBackup, then why did I buy a
VTL? I haven't gained anything from what I see.
Thank you.
- Heathe Kyle Yeakley
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