> >> 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.
>
> That's another reason I'm considering STAC Replica NDM
> (http://www.stac.com/cw/) for desktops and mobile PCs. No tapes!!! What do
> you think?
>
> Regards,
> Orin Rehorst
>
>
> -----Original Message-----
> From: Garin Walsh [mailto:Garin_Walsh AT NOTES.SABRE DOT
> COM]
> Sent: Monday, November 29, 1999 11:50 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: Tape Library Recommendation
>
> 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
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