Orin,

Two things that bit me when planning my current install are that I
underestimated tape usage and the number of drives needed.

1. Unless you run reclaims all the time (see 2. for the downside of this), your
tapes will average about 40% occupancy regardless of collocation usage or not.
On day one you get 100% occ. but over time the reclaimable percentage goes up
reducing the effective storage of your library. So, once you figure out the
number of files you will store and your retention times and whatnot then
multiply that by two to account for the "not yet reclaimed" space on tape. Just
an opinion here but if I had done the x2 I would have met my planned need -
thankfully we have not met our growth plans.....

2.Get at least 3 drives in a library. If you have physical limits on  your disk
pools, database, log, or tape pools and/or more than intermittent restores or
use HSM then you will start having contention between reclamation, database
backups, storage pool backups, and restores. ADSM has a priority scheme for this
through canceling and schedule order but it is frustrating to have processes
wait for tape drives. If you look at the DLT drives some of those mount/seek
waits can be quite long. If you have many clients and a "small" disk pool you
can get a scenario going where every client will want to put at least one file
directly to tape before writing to disk pool. For instance, on a library with
two drives, if you have a reclaim running and client backups start, they will
write to the disk pool. At some point migration will kick off for the disk pool
which will wait for the reclaim to finish. When the disk pool fills all the
pending clients will go into a media wait status. Now everything waits for the
reclaim to finish. When it does, the migration for the disk pool will start - if
you run two migration processes the clients will still wait. When the migration
is done and at least one drive is free, one of the clients will allocate that
drive and start writing its next file to it. Even though there is free space in
the disk pool all the media wait clients will still wait for a tape drive. Each
individual client will mount a tape to dump a file to it before going back to
writing to the disk pool. If you are using a high capacity tape these mounts and
dismounts can be expensive time wise and all the time these tapes are mounting
and dismounting the disk pool is filling again and so it can all happen again.
And again. Worst case you could wind up with a tape mount per file. Ick.

From an opinion standpoint, restores should drive your decision process for
media and tape size. Bigger is not better in some cases. Just image the scenario
where you need to restore a critical file with you CEO watching and have to
explain that it is going to take an hour because there are 5 tape mounts
involved and each has to seek across 75GB of tape surface. If you had the money,
you might want to consider two libraries, large capacity DLT tape for the
storage pool and something with faster access, Magstar for instance,  for the
primary backup pool - just a thought.

Oh, and try to take a class. ADSM is a different beast from rest and in the good
old IBM tradition there is a lot of up-front knowledge necessary to set things
up correctly. Makes future management much easier. The Redbooks are also
helpful.

Garin Walsh
Sabre Inc.





"Robinson, Cris" <Cris.Robinson AT LIBERTYMUTUAL DOT COM> on 11/29/99 11:39:59 
AM

Please respond to "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>

To:   ADSM-L AT VM.MARIST DOT EDU
cc:    (bcc: Garin Walsh)

Subject:  Re: Tape Library Recommendation




Orin...

There are other considerations also. How many inactive versions of files do
you plan to keep? How many deleted version do
you plan to keep. Also, how long do you plan to keep inactive and deleted
copies? Are you archiving at all with ADSM?
Are you planning to do any disaster recovery i.e. off site tape vaulting? It
could make a difference.

I would go DLT from personal exerience. Cost per tape is ~$80 depending on
vendor with 4000 drives you get 40GB, 20 Compressed.
7000's get 70GB and 35 compressed.
For administrative and growth purposes I would go with a Library over a
changer.

StorageTek has the 9730 which can hold up to 28 tapes with 4 DLT drives or
30 tapes with 3 drives.
ATL has a similiar system called the P1000.

DLT 4000 drives for these units run about $5000 or so
DLT 7000 drives run about $10000 ( they hold more data per tape )

DLT 4000's should be fine. I would think anyway.

And you thought you were asking a simple question!


C
__________________________________________________
Cris Robinson
Sr. Technical Analyst
Enterprise Storage Management / TSM (ADSM)
Liberty Mutual Insurance
Portsmouth, New Hampshire
603.431.8400.54837
mailto:cris.robinson AT libertymutual DOT com

        -----Original Message-----
        From:   Orin Rehorst [SMTP:rehorst AT POHA DOT COM]
        Sent:   Monday, November 29, 1999 10:25 AM
        To:     ADSM-L AT VM.MARIST DOT EDU
        Subject:        Tape Library Recommendation

        *       What do you recommend for an entry level library on a
limited >
        budget?
        *
        *       I'm > backing up 8 servers and about 15 users. Could go
conceivably
        up to 10 > servers and 100 users. Max storage of about 250 GB.
                >
                > A single tape drive and a small one-drive library?
                >
                > A small library with two drives?
                >
                > DLT?
                >
                > What brand and model(s)?
                >
                > TIA

        Orin Rehorst
        Port of Houston Authority
        (Largest U.S. Port in foreign tonnage)
        e-mail:  rehorst AT poha DOT com <mailto:rehorst AT poha DOT com>
        Phone:  (713)670-2443
        Fax:      (713)670-2457
        TOPAS web site: www.homestead.com/topas/topas.html