RE: disk subsystem performance question

John,
 We use 7700E. Most all EMC is going out and being replaced by HDS RAID-5. (What it costs is more important that what it does). Everything we have is on RAID-5 these days.
 HDS Techies and our Capacity Planners (who do the disk assignments to Servers) told me the following: The 18GB drives are arranged by 'parity groups' inside the array and are striped at H/W level. Each such group is then chopped off as 7-8GB disk device for the target server (/dev/hdiskXX). Disk devices on the server with the same 'parity group' can be considered as one hard disk. Sys Admins then build the VGs of such hdisks with identical parity group. We then ask them to build LVs for FSs to be used for data and index separation. This scheme has been working well for us for the time being. I am still hoping to someday go back to RAID 1+0. Pl check with your HDS Techies about this 'parity group' theory and see what they are doing for you. Please update us if this theory (as was told to us) works or it was just to pacify us.
 The NV Cache gets immediately saturated. The db size and demand for data will always be way larger than the available cache (and cash;)

 Good Luck..

• Kirti

-----Original Message-----
Sent: Wednesday, April 10, 2002 12:09 PM To: Multiple recipients of list ORACLE-L

Short answer - NO! Nobody's disk subsystem is so fast that no intelligence is required in the layout. This is common vendor blather and one of the most popular myths. I have been hearing it for at least six years - and it still isn't true. Layout still makes a huge difference. RAID levels still make a huge difference. Cache won't solve all your problems (it does help though). I've redone the disk layout on some of the biggest, fastest fully-loaded with cache EMC Syms available that had some "don't worry about it" layout and seen database throughput go up by as much as 8x.

See Gaja's whitepaper on RAID at http://www.quest.com/whitepapers/Raid1.pdf .

Don Granaman
[certifiable oraSaurus]

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Wednesday, April 10, 2002 10:38 AM

> Hi all,
>
> We are running both a Hitachi 7700E and a 9960 disk subsystem here and we
> are getting ready to move our production DBs from the old(7700E) to the
> new(9960) Hitachi. We have had trouble in the past on the 7700E due
to
> disk contention and layout, i.e. we weren't striped across the array
groups
> very well.... this caused pretty poor I/O performance. This has
been
> a learning experience for the DBAs and the SAs here for the logical vs.
> physical aspects of our disks. Anyway, to make a long story short, we
> are ordering disk for the move to the 9960 and we have 2 choices in disk
> sizes - 18GB and 73GB, and 2 choices in RAID - 1+0 and 5. I would like
> to get the smaller, faster 18GB drives in a RAID 1+0 configuration and
> stripe our data across the array groups as wide as possible. However,
I
> am running into objections from the Hitachi people that their system is
> "soooo fast we need not worry about such minor details". I'm having a
> hard time believing that given our I/O problems on the 7700E. Performance
> is given a high priority here.
>
> What I would like to know is others' experience with disk subsystems -
> specifically Hitachi but EMC and others as well.... have you been able
to
> "throw the disk in and forget it" or have you had success in getting to
the
> dirty details? Have you tested or noticed an improvement with
smaller,
> faster drives in a disk subsystem like the Hitachi or have you traveled
> that path and found no noticeable improvement? I'm looking for either
> a) ammunition that my view is correct, or b) I'm wrong and we can get
> bigger drives which will make Enterprise Planning very happy from a $$$
> standpoint because our Hitachi capacity will last longer.
>
> We are running Oracle 8.1.7 / AIX 4.3.3 / Peoplesoft Financials version 8.
> 2 production databases , one 400 GB and the other about 1TB. We've got
> some other production DBs but these are our big guys.
>
> Thanks in advance for any and all input - any help is greatly appreciated.
> I'd be happy to share any info we have found up to this point and our
> experiences on the 7700E as well if anyone is interested - despite the
fact
> I will probably bore you to death :-)
>
> John Dailey
> Oracle DBA
> ING Americas - Application Services
> Atlanta, GA
>
>
>

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Author: Deshpande, Kirti
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