Mehdi and David

My experience is that control path failover is occasionally useful,  the
main instance being where a tape gets stuck in the control path drive,
and the drive is unresponsive to its control path function while it
repeatedly attempts to load the faulty tape. This happened repeatedly on
an old 3584/LTO1 combination where the customer refused to replace the
worn tapes, but continued to depend on them.  However for a small to
medium sized installation with new equipment I am not sure if the cost
is worth the benefit.  Reassigning the TSM library definition to another
control path and restarting TSM can usually work around the problem.

For drives that can be dual attached this may be beneficial for load
balancing, but again this should only be a concern for large
installations or where an interruption to a lage data transfer will have
serious implications, such as creating terabyte-sized individual backups
or stgpool copies of these, and the time window is restricted.

For LTO drives with one path or smaller installations, the extra expense
of data path failover is usually not worth the benefit.  TSM will
normally pick up the error and restart the process anyway, on a
different drive, and the errors that occur in practice are normally
related to the tape rather than the drive or san.  Even so, losing a
single path to single drive does not normally cause TSM to fail though
performance can be degraded.  Total SAN switch failures are rare, and if
they occur there may be data access problems that are more impacting
than access to a tape drive.  My only caveat would be that two drives
are really not enough for a long term TSM installation, even a small
one.  A minimum of three are necessary to provide continued operation
when the inevitable tape gets stuck in a drive.

Regards

Steve.

Steven Harris

TSM and AIX Admin
Seeking AIX or TSM work, Sydney Australia


David McClelland wrote:

Yes: for example, the IBMtape/Atape etc device driver can help your host to
manage data path failover (DPF) for your drives and control path failover
(CPF) for the library's robotics. It can also help with its dynamic load
balancing feature as it tries to ensure that, if multiple paths exist from
host to drive, the least utilised path gets used (depending upon
OS/drive/driver you may need manually to configure this feature, and it may
be at cost). Also consider that drives have different connectivity options -
for example, IBM TS1120/1130 drives can be dual-attached to the SAN thereby
potentially reducing the risk of isolation in event of a single SAN
component failure, however LTO drives only have one fibre connection.

/DMc

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Grigori Solonovitch
Sent: 11 October 2009 12:09
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] MPIO for tape libraries

Of course, you need MPIO for fiber optics tape drives. It is not only high
availability. It is better performance as well.

Grigori G. Solonovitch

Senior Technical Architect

Information Technology  Bank of Kuwait and Middle East  http://www.bkme.com

Phone: (+965) 2231-2274  Mobile: (+965) 99798073  E-Mail:
G.Solonovitch AT bkme DOT com

Please consider the environment before printing this Email


-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Mehdi Salehi
Sent: Sunday, October 11, 2009 1:57 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] MPIO for tape libraries

Hi,
Does it make sense to have MPIO for tapes? As tape libraries play an
important role in TSM, their connection to hosts and specially to TSM server
itself should be a reliable one. Should I expect to have link failover
and/or load balancing for tape drives (something like SDDPCM, HDLM, ... for
disk subsystems)?

Thanks

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