Hi,
some have reported that collocation OFF causes restore to be very slow.
It is generally true.
In some situations, collocation OFF can even speed restores.
Assuming tape library with more than one tape drive available for restore,
and restore is configured to allow for more than one tape mounts,
and node data fit typically on one tape,
having collocation turned ON causes only one drive to be used for restore,
while collocation OFF will allow for more tape drives be used in paralell.
Speaking about tapes,
restore time depends on data read time, data seek time and tape mount time.
Collocation ON will cause everything to happen sequentially,
collocation OFF will allow for paralell usage of ressources.
This will help if your
amount of tapes in storage pool concerned is low (10-50)
amount of tape drives is high (2-4)
amount of data migrated per node during one migration is high (you use large
primary
disk storage pool), or when you have few but large files to restore.
In any other case
all warnings about collocation OFF causing restores to take forewer are
true.
Regards
Juraj Salak
-----Ursprüngliche Nachricht-----
Von: Paul Zarnowski [mailto:vkm AT CORNELLC.CIT.CORNELL DOT EDU]
Gesendet: Montag, 07. April 2003 16:54
An: ADSM-L AT VM.MARIST DOT EDU
Betreff: Re: Turning collocation off?
If you want to increase the utilization of your tape pool, you can allocate
fewer tapes to it. The number you allocate will depend on what tradeoff
you want to make between tape utilization and collocation effectiveness.
The big drawback to turning collocation off is that it will slow down
restores due to increased tape mount activity during the restore
process. Over time, it will get worse and worse.
At 03:17 PM 4/7/2003 +0100, Farren Minns wrote:
>Hi All
>
>Running TSM 4.2.2.12 on Sol 2.7 server. At present we use collocation on
>the tapes within the TAPEPOOL (i.e. in the 3494 library). We are getting to
>a point where the number of available scratch tapes in the lib is getting
>small and I'm considering turning collocation off. We always seem to have
>about 25-30 tapes that are under 10% used which seems like a large waste of
>space.
>
>I understand that collocation speeds things up in the event of a system
>restore, but this is something that we rarely (in fact, never in the last
>two years) need to do and anyway, the library can handle all the tape
>mounts and stuff.
>
>This is all rather long winded, but my question is simple. Are there any
>things I should be aware of before setting collocation to NO. i.e., are
>there any possible problems I may encounter.
>
>Many thanks
>
>Farren Minns - John Wiley & Sons Ltd
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Paul Zarnowski Ph: 607-255-4757
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