Re: hard disk configuration question

• Steve McClure <smcclure_at_usscript.com> on 12/18/01 11:00:22 -0800

> We are in the process of buying new hardware, and our original configuration
> called for 10 18 GB drives in a Hitachi disk array cabinet. We are getting
> some sales pressure to change this to 5 36 GB disks. Now I was planning to
> spread our DB out over as many mirrored pairs as possible, or maybe even
> including one RAID1+0 array. The sales folks at Hitachi are telling us that
> with their new drive array technology, spreading our Data files over as many
> disks as possible is not necessary. I am supposed to talk to one of their
> engineers in an hour or so.
>
> I am just wondering if there really is some magic bullet technology I have
> missed out on, or is there sales guy full of hooey?
>
>
> They are also pushing the presence of two internal(not in the drive cabinet)
> drives as alleviating any space concerns. I am wondering what I can use
> those drives for. I don't think I want to software mirror them, but maybe
> Sun does this better than I think. Without some kind of redundancy I am
> reluctant to use these disks for any DB purposes. Any thoughts here are
> appreciated as well.

You are almost always better off with more spindles to spread the load over. With fewer disks you get the same total storage but less flexability in how the I/O is partitioned between devices. Since Oracle is such an I/O hog the added flexability can be a real lifesaver.

Hitachi's claim that there isn't any benefit to spreading out the I/O may be valid with huge amounts of cache. The technology for disk I/O manglement is always improving, so is the quantity of... er... "hooey" available from sales reps; the answer to your question is probably "both" :-)

Personally I'd go with more disks using RAID5 w/ a stripe size equal to the O/S page (e.g., 4x1K or 8x1b for a 4KB file i/o page or 8x1k for an 8K system page). This avoids extra overhead from the RAID5 parity writes (you have to hit all the disks every time anyway) and gives you back a lot of extra storage over mirroring. Using the RAID5 w/ a reasonable stripe also allows you to spread the I/O over multiple RAID's to balance the load -- sine the RAID set is the "PV" managed by your LVM system. The extra disks come in handy at this point because you can create more RAID sets for balancing the load.

In theory if you have enough cache none of the disk parameters matter at all. Then it depends largely on your budget for cache and how well the current Hitachi controllers manage it. If you don't have infinte faith in their cache management system then more disks is the better bet.

--
Steven Lembark                              2930 W. Palmer
Workhorse Computing                      Chicago, IL 60647
                                           +1 800 762 1582
-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: 
  INET: lembark_at_wrkhors.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).