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How much slower is RAID 1 than no RAID at all? I have heard that RAID 1 provides peace of mind (because of mirroring) but gives slower write (not read) performance.

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    It's pretty well explained on wikipedia, en.wikipedia.org/wiki/Standard_RAID_levels#RAID_1, so you should read that first, since the question while it makes sense, doesn't make sense to ask. You're going to Raid 1 for the redundancy, taking a known performance hit. How much hit depends on other factors like how many write heads, disk speeds, and even more. May 13 '12 at 2:35
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Depends whether you are dealing with hardware RAID or software RAID and what the circumstances are (e.g. controller being used, controller memory, buffer sizes).

Generally you will see a performance hit using software RAID. With a decent hardware RAID controller, depending on the sizes of files being written, you will see little to no difference as the files can be buffered into controller memory then written at a later time.

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    And then there's what's known as 'fake' RAID. This is used by Intel desktop chipsets. I'm using it right now, and I can say there's a rather large performance hit for me (RAID 1) - especially when it's verifying/repairing (does that a lot, usually after 'unsafe' shutdown) or rebuilding (occasionally).
    – Bob
    May 13 '12 at 2:05

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