>
> On Fri, 1 Sep 1995 14:38:22 EDT Paul Zarnowski said:
> >We don't have anywhere's near 1.4T of data, but we do have 250 machines.
> >I know our avg filesize is much smaller than 40Kb, so the number of files
> >we manage in our ADSM database is correspondingly higher.  I think we
> >have about 3 million files in our db now, and about 18.5 million database
> >records.  We run on an RS/6000, 2 channels of disks.
> >I suspect it is important to spread your db on as many spindles as you can,
> >to optimize performance.  We haven't done that yet.  We have 2 duplexed 
> >dbvols
> >on 4 different drives and 2 different channels.  We do see a bit of I/O wait
> >(as reported by the unix sar/sag commands).  I'd be interested in hearing
> >what others think about whether faster disks would help aleviate I/O wait
> >or not.  I suspect much of the wait is due to seeking, and not so much to
> >actually transferring the data, so I'm not sure that faster disks would
> >help.  We're currently using Seagate Barracuda's now.
> >
> >If you think you'd find it useful to talk, feel free to e-mail or call me.
> >..Paul
> >
> >Paul Zarnowski                     Phone:   607/255-4757
> >Cornell Information Technologies   Fax:     607/255-6523
> >Cornell University                 US Mail: 315 CCC, Ithaca, NY 14853-2601
>
> Has anyone considered the usage of RAID disk arrays for the ADSM database
> volumes?  It would seem that the higher I/O rates possible from the RAID
> array would make an them an appealing prospect as well as the fact that
> some array controllers now come with a variable amount of disk cache memory.
> While the cache would probably prove useless for read data, a small amount
> of write cache space could prove itself to be very valuable when a few
> dozen clients are all running at the same time.
>
> The ability to dynamically rebuild data from a failed volume also strikes
> me as being useful as it could be used to avoid having to keep the database
> copy volumes (although you do suffer downtime while the volume is being
> rebuilt which you wouldn't suffer by using database copy volumes).

Normally you would not have downtime while a volume is being rebuilt
on a RAID device.  We have tested several RAID boxes here at the CSC
and all of them will rebuild a failed drive with no down time.  You
must generally decide how much of the controllers time you want to
dedicate to rebuild of the failed drive and how much to normal IO.
After a drive has failed, the system will run in a degraded mode if
the RAID group is a level 5 or level 3 protection.

>
> ---
> Keith A. Crabb         Keith AT UH DOT EDU
> University of Houston  Operating Systems Specialist +1-713-743-1530
>


--
    Mike Dahl                                   Commercial Systems Center
    Mike Dahl                                   Commercial Systems Center
    dahl AT clamsouth DOT com                ''``      2201 Donley Dr Suite 395
    (512) 719-3724 ext 104            (o o)     Austin  TX 78758
+----------------------------------oo0-(_)-0oo------------------------------+
|    Life is what happens to you when you're too busy making other plans.   |
+---------------------------------------------------------------------------+
|            Today is the tomorrow you worried about yesterday.             |
+---------------------------------------------------------------------------+
    Usual disclaimers apply....