Re: databases and RAID ...
От | Fred Moyer |
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Тема | Re: databases and RAID ... |
Дата | |
Msg-id | ILEMKFGEMKDJNPOGGNCKAEAKDCAA.fred@digicamp.com обсуждение исходный текст |
Ответ на | Re: databases and RAID ... (Peter Eisentraut <peter_e@gmx.net>) |
Ответы |
Re: databases and RAID ...
(Ragnar Kjørstad <postgres@ragnark.vestdata.no>)
|
Список | pgsql-admin |
<adding my $0.02> JBOD : just a bunch of disks, not raid in my opinion Raid 0 : striping over disks, no redundancy, hence the Redundancy in Redundant Arrays of Independent Disks is zero. Raid 1 : Mirroring, full redundancy, Redundancy 1(00%) Raid 4: see thread Raid 5: see thread,Striping across multiple disks with parity. You have one spare drive, 3 drives minimum, recommend more cause raid-5 is SLOW Raid 10: A mirrored pair of striped arrays (1+0). from working with various raid controllers (ide and scsi) here is my feedback (please rebuke me if needed as I'm sure others on this list have more experience). Performance (fastest->slowest) hardware raid -> software raid raid 0 -> 10 -> 1 -> 5 Redundancy (most -> least) hardware raid -> software raid 10, 1 -> 5 -> 0 some people say raid 5 is the most redundant but if you have over seven disks your change of two drives failing becomes a statistical reality, hence raid 5 is best suited for arrays of 5-8 drives. RAID 10 and 1 are both mirrored but can be expensive. raid 0 is the fastest but don't count put mission critical data on it - add another n disks and make it raid 10. IDE vs SCSI: I have run both controllers and have found both perform well. The stripe size for raid 10 and 0 is important - make it as large as possible for databases (256k on scsi and 1 MB on ide) since you want the disk heads to read as much as possible before seeking again. for databases use scsi if you can - use ide for streaming audio/video. databases performance relies on being fast at random reads/writes and that's where scsi wins. > Is there any rhyme or reason to the various "RAID n" designations? > Or were they just invented on the spur of the moment? The paper that introduced the term RAID used a numerical classification for the various schemes. (So I guess the answer is yes.) The traditional levels are: 0 Nonredundant 1 Mirrored 2 Memory-style ECC 3 Bit-interleaved parity 4 Block-interleaved parity 5 Block-interleaved distributed parity [Hennessy & Patterson] There are also other levels. One poster talked about RAID 10 which appears to be a mirrored RAID 5. -- Peter Eisentraut peter_e@gmx.net ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
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