Michael,

I would choose 2.  Using JBOD disks build a cachepool with enough space for 
incrementals.  With the rest of it built on RAID5, create onlinefile with 
devclass file.  Choose a volume size of 25GB and create all the volumes 
manually rather than having TSM create them for you on the fly.  This way you 
avoid fragmentation.

You might also choose to use all devclass file pool space and send data 
directly there instead of using the cachepool.  I would decide to do it that 
way if I didn't have lots of clients backing up simultaneously as that pattern 
is very hard on a RAID5 array.

Finally, I would target only that data that would really benefit from this type 
of storage.  Probably file servers or the like.  I wouldn't use it for large 
things, probably, like databases or Exchange data.  That will restore just as 
fast from tape as from disk.

We routinely build our STORServers with a complete mix: cachepool JBOD on fast 
disk, onlinefile RAID5 or relatively slower SATA disk, and onlinepool LTO4.  
With this you can optimize both backups and restores.

One last thing: you really need to use devclass file on the bulk of the storage 
as the disk device class does not provide space reclamation with the file 
device does.

Thanks,

Kelly Lipp
CTO
STORServer, Inc.
485-B Elkton Drive
Colorado Springs, CO 80907
719-266-8777
www.storserver.com


-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of 
Michael Green
Sent: Friday, November 14, 2008 3:19 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] Best use of disk storage

Bright minds,

If you are given 20T of disk space, how would you use it in TSM 5.3
environment in context of speeding up restores?
1. Would you create large disk pools with CACHE=y or..
2. Would you create disk pools sized to accommodate routine
incrementals only with the rest of the space dedicated to devc=FILE
stgpools for staging? (i.e. building a hierarchy such as disk -> file
-> tape)


--
Warm regards,
Michael Green