Probably what happened was the following:
1) 4 buta sessions start (didn't have to be buta), all go to disk
storage pool
2) disk stgpool hit 60% threshold, 1 migration process started, mounts
one tape
3) 4 session fill disk pool faster than one mig process can drain it
(depends on network throughput and tape technology, and number of
sessions/migprocesses), %util climbs from 60% to 100%
4) as %util approaches 100%, each session in turn finds the disk pool
full, allocates a mount pount, and mounts a tape and sends the next file
to the tape stgpool
(as each file is sent to the server, the server evaluates whether there
is enough space in the backup copy group's destination storage pool has
enough space for the next file; when there isn't, the next file is sent
to the destination stgpool's next storage pool)
5) although the sessions may switch back to the diskpool when the mig
process makes space, they quickly (within two minutes?) fill it again
and go back to tape, keeping the tapes mounted.
6) when the sessions complete, the mig process clears out the diskpool
You can confirm this by recreating the situation and issuing a 'q se
f=d' to see what the media status is. It will show whether the session
itself has a a tape mounted.
You can cure the situation by setting the allowable migration processes
higher on the disk stgpool, assuming that multiple migration processes
can keep up with the 4 streams of backup sessions (imagine 4 sessions
coming in across 4 different 100baseT network connections to a striped
SSA disk pool being drained by 4 Exabyte 8200 8mm tape drives :-). ADSM
migrates by node/filespace, does you multi-stream buta backup create
multiple pseudo-filespaces? If a disk stgpool has only one filespace
from one node, only one mig process will run regardless of the setting
of 'mig process' for the stgpool.
Cheers...
Bruce
"J. O'Neall" wrote:
>
> I need some help understanding how ADSM uses tapes, especially when there
> is no available disk storage pool.
>
> I've just started trying the use of the buta interface from AFS to ADSM.
> I'm not sure my question is restricted to the use of buta, tho, so will
> those who know about ADSM's use of tapes please keep reading.
>
> Yesterday (yes, Sunday), I backed up about 35GB of disk via 4 buta ports (2
> each on 2 stations). All files went to a 4GB disk storage pool, with
> reclamation set to hi/lo=60/30. It worked, but I saw ADSM with up to 5
> tapes mounted for the single migration process which lasted for the duration
> of the backup. My feeling was that it wanted a tape for each buta "stream",
> if I may call it that.
>
> So I restricted the tape device class to only one tape and started 2 streams
> of backup. One got its tape and went ahead to completion. The other got
> stuck. I had to open the device class up to 2 tapes so it could mount a
> second one, then the 2nd stream came to life. But now, 10 minutes later,
> both tapes are still mounted, and the tape dismount period is set to 2
> minutes.
>
> Can anybody help me to understand what's going on?
>
> Thanks in advance. John
>
> -----
> John O'Neall
> Centre de Calcul de l'IN2P3
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