Re: SCSI vs SATA
От | Rod Taylor |
---|---|
Тема | Re: SCSI vs SATA |
Дата | |
Msg-id | B0FD3588-39A6-4791-BDEA-2B0A506B8FF3@gmail.com обсуждение исходный текст |
Ответ на | Re: SCSI vs SATA (Andreas Kostyrka <andreas@kostyrka.org>) |
Список | pgsql-performance |
On 4-Apr-07, at 8:46 AM, Andreas Kostyrka wrote: > * Peter Kovacs <maxottovonstirlitz@gmail.com> [070404 14:40]: >> This may be a silly question but: will not 3 times as many disk >> drives >> mean 3 times higher probability for disk failure? Also rumor has it >> that SATA drives are more prone to fail than SCSI drivers. More >> failures will result, in turn, in more administration costs. > Actually, the newest research papers show that all discs (be it > desktops, or highend SCSI) have basically the same failure statistics. > > But yes, having 3 times the discs will increase the fault probability. I highly recommend RAID6 to anyone with more than 6 standard SATA drives in a single array. It's actually fairly probable that you will lose 2 drives in a 72 hour window (say over a long weekend) at some point. > Andreas >> >> Thanks >> Peter >> >> On 4/4/07, david@lang.hm <david@lang.hm> wrote: >>> On Tue, 3 Apr 2007, Geoff Tolley wrote: >>> >>>> >>>> Ron wrote: >>>>> At 07:07 PM 4/3/2007, Ron wrote: >>>>>> For random IO, the 3ware cards are better than PERC >>>>>> >>>>>>> Question: will 8*15k 73GB SCSI drives outperform 24*7K 320GB >>>>>>> SATA II >>>>>> drives? >>>>>> >>>>>> Nope. Not even if the 15K 73GB HDs were the brand new Savvio >>>>>> 15K >>>>>> screamers. >>>>>> >>>>>> Example assuming 3.5" HDs and RAID 10 => 4 15K 73GB vs 12 >>>>>> 7.2K 320GB >>>>>> The 15K's are 2x faster rpm, but they are only ~23% the >>>>>> density => >>>>>> advantage per HD to SATAs. >>>>>> Then there's the fact that there are 1.5x as many 7.2K >>>>>> spindles as 15K >>>>>> spindles... >>>>> Oops make that =3x= as many 7.2K spindles as 15K spindles... >>>> >>>> I don't think the density difference will be quite as high as >>>> you seem to >>>> think: most 320GB SATA drives are going to be 3-4 platters, the >>>> most that a >>>> 73GB SCSI is going to have is 2, and more likely 1, which would >>>> make the >>>> SCSIs more like 50% the density of the SATAs. Note that this >>>> only really >>>> makes a difference to theoretical sequential speeds; if the >>>> seeks are random >>>> the SCSI drives could easily get there 50% faster (lower >>>> rotational latency >>>> and they certainly will have better actuators for the heads). >>>> Individual 15K >>>> SCSIs will trounce 7.2K SATAs in terms of i/os per second. >>> >>> true, but with 3x as many drives (and 4x the capacity per drive) >>> the SATA >>> system will have to do far less seeking >>> >>> for that matter, with 20ish 320G drives, how large would a >>> parition be >>> that only used the outer pysical track of each drive? (almost >>> certinly >>> multiple logical tracks) if you took the time to set this up you >>> could >>> eliminate seeking entirely (at the cost of not useing your >>> capacity, but >>> since you are considering a 12x range in capacity, it's obviously >>> not your >>> primary concern) >>> >>>> If you care about how often you'll have to replace a failed >>>> drive, then the >>>> SCSI option no question, although check the cases for hot- >>>> swapability. >>> >>> note that the CMU and Google studies both commented on being >>> surprised at >>> the lack of difference between the reliability of SCSI and SATA >>> drives. >>> >>> David Lang >>> >>> ---------------------------(end of >>> broadcast)--------------------------- >>> TIP 1: if posting/reading through Usenet, please send an appropriate >>> subscribe-nomail command to majordomo@postgresql.org so >>> that your >>> message can get through to the mailing list cleanly >>> >> >> ---------------------------(end of >> broadcast)--------------------------- >> TIP 3: Have you checked our extensive FAQ? >> >> http://www.postgresql.org/docs/faq > > ---------------------------(end of > broadcast)--------------------------- > TIP 5: don't forget to increase your free space map settings
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