Re: [ADSM-L] MPIO for tape libraries

Mehdi,

>>> Does defining logical tape drives helps eliminating this single point of
failure such that if during client backup the fiber connection of drive
fails, another tape drive in the library takes over the operation?

Okay, the quote from the Redbook below may have misled you in this case: a
'logical tape library' as you describe below is quite different to the
concept you describe as a logical tape drive, it is how IBM describe their
library partitioning. Here, creating 'logical libraries' (i.e. a library
partition) will allow you to share a single physical library amongst, for
example, Netbackup, Mainframe and TSM applications and the partitioning is
managed by the library itself (e.g. with ALMS in a TS3500/3584) and has
nothing to do with any virtualisation/logical definitions within TSM or the
OS. The tape drives themselves here are not virtualised: you're still
accessing a *physical* tape drive device, and a failure of a physical LTO
drive, or the path to it, will still result in that path/drive going offline
- potentially interrupting a data movement operation, although as Steven has
also pointed out, TSM's normally pretty hot on these and may retry the
operation on a different drive.

Hope that helps,

/DMc
London, UK



-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Mehdi Salehi
Sent: 12 October 2009 06:42
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] MPIO for tape libraries

For logical tape libraries, please look at this excerpt from SG24-5946-06:
" Multiple logical libraries are an effective way for the library to
simultaneously back up and
restore data from heterogeneous applications. For example, the library can
be partitioned so
that it processes:

   - Commands from Application 1 (about Department X) in Logical Library A
   - Commands from Application 2 (about Department Y) in Logical Library B
   - Commands from Application 3 (about Department Z) in Logical Library C

In this configuration, the storage slots and drives in each logical library
are dedicated to that
library and are not shared among other libraries. Commands issued by the
applications travel
to the library through three unique control paths. Thus, the data processing
for:

   - Department X is confined to the storage slots and drives in Logical
   Library A
   - Department Y is confined to the storage slots and drives in Logical
   Library B
   - Department Z is confined to the storage slots and drives in Logical
   Library C"

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06:39:00

-----Original Message-----
From: David McClelland [mailto:tsm AT networkc.co DOT uk]
Sent: 11 October 2009 18:18
To: 'ADSM: Dist Stor Manager'
Subject: RE: [ADSM-L] MPIO for tape libraries

I'm not quite sure I know what you mean by 'defining logical tape drives',
without a VTL or somesuch. Can you expand technically upon what you mean?

>From my experience, the majority of failures involving tape drives have been
down to drive/head mechanics failure or tape cartridge errors (although I
note that this seems to be increasingly uncommon these days), rather than
physical fiber component failure. In these instances, any amount of
multi-pathing can't help and you need to make sure that you have enough
spare capacity in your library/design to cope, and an alerting/support
process in place which can recognise it and get it resolved as quickly as
possible. Given that most of your backup clients will (presumably) initially
write to TSM-managed disk storage pools (except SAN Storage Agents and
perhaps NDMPs etc) hopefully a drive failure won't have a direct impact upon
a client backup data integrity, as TSM tends to be pretty precious about
this when performing migrations/data movement operations involving tapes.

/DMc

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Mehdi Salehi
Sent: 11 October 2009 17:13
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] MPIO for tape libraries

Thanks David, you made a good point about single fiber connections of LTO
drives. Does defining logical tape drives helps eliminating this single
point of failure such that if during client backup the fiber connection of
drive fails, another tape drive in the library takes over the operation?