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On Thu, 2006-03-02 at 17:19 +0100, Marton Gabor wrote: |
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> Hi! |
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> |
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> Thank you all for the fast replies, you helped me a lot. Unfortunately |
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> we cannot afford a HW RAID card, so I have to make it with software RAID. |
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> Now I have the idea to use RAID5 and if I get the picure rigth I need |
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> let's say a ~100MB /boot in RAID1, 512MB swap not in RAID on every disk, |
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> and I can build a RAID5 from the rest of the storage space, and will be |
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> able to use 750GB-(/boot*4)-(swap*4) and the 4th HD will store the |
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> so-called parity information. |
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Not quite. |
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With Raid3 and Raid4 the parity is stored on an extra disk, so you have: |
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[data][data][data][data][parity] |
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|
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Raid5 spread the parity across all disks, so loss of any single disk |
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will not cause any data loss. The data on that disk can be rebuilt |
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easily, but two disk failures are fatal. |
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Example for a 4-disk raid5: (d=data, P=parity) |
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1234 |
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dddP |
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ddPd |
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dPdd |
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Pddd |
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... |
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So with 4 disks you get 3 capacity, but there is no dedicated place for |
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parity! |
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-- |
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Stand still, and let the rest of the universe move |
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