Another factor to consider on EMC is the RAID type. According to their
white paper, "EMC Backup Storage Solutions: Backup-to-Disk Guide with IBM
Tivoli Storage Manager", the preferrred RAID type is **_RAID-3_**. Our
Clariion requires five or nine disks to implement that RAID level. With a
pod full of SATA disks we implemented two five-disk RAID-3 arrays and one
four-disk RAID-5 array for use as TSM disk pools. We consistently see
40-50 MB/s with the RAID-3 LUNs, while the RAID-5 LUN seems to max out at
about 22 MB/s. I understand that drive count is a factor in all this, but
I doubt that the difference of one disk's media would yield a 50% loss of
performance. However, in subsequent discussions with their engineers
they've stated that the Clariion internal "Flare" code is optimized for
RAID groups made with (4 x n + 1) disks; meaning 5, 9, 13, etc. Using any
other drive count in a RAID group compromises that optimization. At some
point, we will probably remake some of our RAID groups, including that one
RAID-5 array.
Tab Trepagnier
TSM Administrator
Laitram, L.L.C.
"ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU> wrote on 05/11/2005
01:54:04 PM:
> Andy Huebner wrote:
>
> >We use RAID 5 (5+1) on a Clariion using 146GB drives. We peak the
> drives at over 55MB/sec, sustained speed is over 45MB/sec. How fast
> are you reading and writing to your disks? If it is faster than
> your SAN storage can read and write from RAID 5 then mirroring or
> striping is a better choice, although I would not use unprotected disks.
> >
> >Andy Huebner
> >
> > -----Original Message-----
> >From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On
> Behalf Of Luc Beaudoin
> >Sent: Tuesday, May 10, 2005 7:47 AM
> >To: ADSM-L AT VM.MARIST DOT EDU
> >Subject: [ADSM-L] Diskpool question
> >
> >My diskpool is on a SAN, I have to increase the size cause I'm taking
> >about 450GB per day and my diskpool is 350GB...
> >
> >Is there a RAID issue for performance .... right now my diskpool is on
a
> >RAID5 ... should I still use RAID5 or there a better RAID
configuration??
> >
> >thanks
> >
> >Luc
> >
> >
> >This e-mail (including any attachments) is confidential and may be
> legally privileged. If you are not an intended recipient or an
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> >Thank you.
> >
> >
> >
> >
> Just for information, EMC did not optimize the FlareCode on Clariion for
> RAIDGroup with even disk (3+1, 5+1, ...) so It could be better to use
> 4+1, 6+1, 8+1 RAIDGroup (See Clariion Best Practises on Powerlink). We
> use a 4+1 configuration and during our backup database we have a
> sustained speed of 70-80 MB/s.
>
> Stripe on each disk is 64KB lenght, for four disk you have a full data
> stripe of 256KB (4x64KB + 64KB Parity) and th default LTG size of AIX
> Volume Group is 128kB.
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