[Veritas-bu] assigning only a portion of tape drives to media servers

[Ed Wilts]

On Tue, Jan 6, 2009 at 11:20 AM, Geyer, Gregory <Gregory.Geyer at avnet.com>wrote:

>  We have all our tape drives (20) assigned to all our media servers (3
> main ones, and ~45 that server as SAN media servers, backing only themselves
> up).
>
> Dealing with tape drive throughput issues and we've had a Brocade support
> person tell us that this setup is not ideal and that even when a tape drive
> has been granted to a host and it starts to use it, that its checking on the
> other tape drives prevents good throughput.  He says to only assign about 4
> drives per media server.
>
> This does not seem right to me, but hey, I'll check out anything.  My
> understanding is that 6.5 (we're at 6.5.2a, about to go to 6.5.3) has a
> centralized device database and that the design of a SCAN_HOST performs the
> gatekeeper roll for the tape drives.
>

Pre-6..0, every host was responsible for managing the tape drives, and the
master would constantly poll each media server for what was going on.
Starting at 6.0, the master took total responsibility for it and simply
tells the media server which media to mount on which device.  Media servers
became a lot dumber, and that's actually a good thing.

If you have any opinions on Brocade's theory (or at least our SAN guy's
> interpretation of it - this is all 2nd hand) I'd be happy to receive it.
>

I think his data is dated and the suggested changes are not going to help
with throughput at all but hurt you in device availability as you've already
discovered.  As a result, the total amount of data you'll be able to push
through will decrease, not increase.

>

    .../Ed

Ed Wilts, RHCE, BCFP, BCSD, SCSP, SCSE
ewilts at ewilts.org
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