ADSM-L

Re: 3 layer storage hierarchy

2006-10-24 02:38:31
Subject: Re: 3 layer storage hierarchy
From: Remco Post <r.post AT SARA DOT NL>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Tue, 24 Oct 2006 08:36:53 +0200
Andrew Raibeck wrote:
> Sorry folks, I misremembered... the scenario I am thinking of is described
> by APAR IC33719. The Admin Reference also contains this info for the
> NEXTSTGPOOL parameter in the DEFINE STGPOOL info for sequential access
> pools.
>
> --------------------------------------------------
> Specifies a primary storage pool to which files are migrated. You cannot
> migrate data from a sequential access storage pool to a random access
> storage pool. This parameter is optional.
>
> If this storage pool does not have a next storage pool, the server cannot
> migrate files from this storage pool and cannot store files that exceed
> the maximum size for this storage pool in another storage pool.
>
> When there is insufficient space available in the current storage pool,
> the NEXTSTGPOOL parameter for sequential access storage pools does not
> allow data to be stored into the next pool. In this case the server issues
> a message and the transaction fails.
>
> For next storage pools with a device type of FILE, the server performs a
> preliminary check to determine whether sufficient space is available. If
> space is not available, the server skips to the next storage pool in the
> hierarchy. If space is available, the server attempts to store data in
> that pool. However, it is possible that the storage operation could fail
> because, at the time the actual storage operation is attempted, the space
> is no longer available.
> --------------------------------------------------
>
> TSM should do up-front space checks, and traverse as many "next" storage
> pools as needed to find a target storage pool. But once TSM starts to
> actually store the data in that pool, an out-of-space condition in that
> pool could cause the operation to fail.
>

In this case we should (given that enough space is available in the
final tapepool) never get the message 'server out of storage-space'. Or
doesn't TSM pre-allocate space for a transaction on sequential storage
like it does on random access disk? We could get messages like 'size
estimate exceeded...' and 'media mount not possible', which are
disastrous in case of TDP backups, but 3 layers should work.

I'll rebuild things on my test-server and try to replicate. Maybe I
should actually open a PMR for this.

--
Met vriendelijke groeten,

Remco Post

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