RAID 5 write performance
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From: Tom Del Rosso on 17 Jun 2008 01:06 Since it's striped I would expect RAID 5 to be faster than RAID 1 generally, but I've read some vague references (in this link and elsewhere) to lower write performance in 5 than in 1. Why would that be so? http://www.msexchange.org/articles/Transaction-Logs-Lifeblood-Exchange.html -- Reply in group, but if emailing add another zero, and remove the last word.
From: Igor Batinic on 17 Jun 2008 03:23 Hi! Tom Del Rosso wrote: > Since it's striped I would expect RAID 5 to be faster than RAID 1 generally, > but I've read some vague references (in this link and elsewhere) to lower > write performance in 5 than in 1. Why would that be so? > > http://www.msexchange.org/articles/Transaction-Logs-Lifeblood-Exchange.html Indeed, RAID 5 (usually) is much slower that RAID 1 in such cases, especially if you use RAID 5 array for such a purpose without a lot of cache, battery backup etc. RAID 5 is not recommended array for transaction logs not only in Exchange environment, but also in all other environments. Best regards, Iggy
From: Arno Wagner on 17 Jun 2008 09:32 Previously Tom Del Rosso <td_03(a)att.net.invalid> wrote: > Since it's striped I would expect RAID 5 to be faster than RAID 1 generally, > but I've read some vague references (in this link and elsewhere) to lower > write performance in 5 than in 1. Why would that be so? > http://www.msexchange.org/articles/Transaction-Logs-Lifeblood-Exchange.html Unkess you rite exactly in stripe size, in RAID5 you have to read the rest of the stripe from the other drives, before writing (to do the checksum). With RAID1 you just write, regardless of size. This is mostly an issue for small accesses. Arno
From: Tom Del Rosso on 17 Jun 2008 09:44 "Igor Batinic" <_ime_._prezime_(a)email.htnet.hr> wrote in message news:g37op6$8pq$1(a)localhost.localdomain > Hi! > > Tom Del Rosso wrote: > > Since it's striped I would expect RAID 5 to be faster than RAID 1 > > generally, but I've read some vague references (in this link and > > elsewhere) to lower write performance in 5 than in 1. Why would > > that be so? > > > > http://www.msexchange.org/articles/Transaction-Logs-Lifeblood-Exchange.html > > Indeed, RAID 5 (usually) is much slower that RAID 1 in such cases, > especially if you use RAID 5 array for such a purpose without a lot of > cache, battery backup etc. > > RAID 5 is not recommended array for transaction logs not only in > Exchange environment, but also in all other environments. But why is it slower in write mode? Does the controller write the parity multiple times even when all the drives are modified? -- Reply in group, but if emailing add another zero, and remove the last word.
From: Tom Del Rosso on 17 Jun 2008 11:23
"Arno Wagner" <me(a)privacy.net> wrote in message news:6bpsmpF3d9kneU2(a)mid.individual.net > > Unkess you rite exactly in stripe size, in RAID5 you have to > read the rest of the stripe from the other drives, before > writing (to do the checksum). With RAID1 you just write, > regardless of size. This is mostly an issue for small accesses. Thanks. -- Reply in group, but if emailing add another zero, and remove the last word. |