RE: Hitachi 9000 (was RE: 2GB or not 2GB )

  • From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
  • To: <kmoore@xxxxxxxxxxxx>, <kevinc@xxxxxxxxxxxxx>
  • Date: Mon, 11 Sep 2006 15:56:14 -0700

Here is a problem I had in a similar situation - our Netbackup server
was using some space on a SAN for its disk staging pool (before writing
backups to tape).  Some of our databases were on the same SAN and would
have terrible I/O performance from time to time - turned out it was
because we were relying heavily on the SAN cache since we were running
RAID5, and when the backups to disk would run, they would consume all
the cache on the SAN and force the databasee to wait on the terribly
slow RAID5 writes to disk.  The solution was to disable caching for the
backups on the SAN.  

Lessons learned: beware of RAID5 (as you seem to be already); beware of
your dependency on cache if you decide to use RAID5 despite the dangers;
and, beware of sharing disk subsystems - you never know who/what might
cause your database performance to take a dive.

> -----Original Message-----
> From: oracle-l-bounce@xxxxxxxxxxxxx 
> [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Keith Moore
> Sent: Monday, September 11, 2006 3:10 PM
> To: kevinc@xxxxxxxxxxxxx
> Cc: oracle-l
> Subject: RE: Hitachi 9000 (was RE: 2GB or not 2GB )
> I check my data and found it is actually 102 GB in 66 minutes 
> for a rate of 26 MB/sec for a full table scan. "Sequential 
> reads" are much slower, around 8-10 MB/sec.
> Here is what I know about the architecture:
>   Two Hitachi SANs
>   2 SANs are shared by 4 Sun 15K servers
>   Disks are 146 GB each
>   Each disk split into 35 GB Logical Volumes
>   8 disks in a logical disk group (Raid 5 w/ 128K stripe)
>   2 HBA per SAN. I think 1Gb, but not sure
>   Veritas file system
>   56 GB read/write cache
> I know Raid10 would be better, but Raid5 is the corporate 
> direction. The other problems seem to be that the disks are 
> shared by multiple databases and possibly the stripe size.
> Any comments would be appreciated.
> Keith
> >
> > That is 113MB/s.  You wouldn't happen to have 1Gb HBAs would you?
> > Is this data striped across, say, 10 spindles?
> >
> --
> //

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