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" <[email protected]> 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:[EMAIL PROTECTED] On > Behalf Of Luc Beaudoin > >Sent: Tuesday, May 10, 2005 7:47 AM > >To: [email protected] > >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 > authorized representative of an intended recipient, you are > prohibited from using, copying or distributing the information in > this e-mail or its attachments. If you have received this e-mail in > error, please notify the sender immediately by return e-mail and > delete all copies of this message and any attachments. > >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.
