-- Steve McClure <[EMAIL PROTECTED]> 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
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