21 lines
1.2 KiB
Markdown
21 lines
1.2 KiB
Markdown
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title = "So why do I need a backup?"
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description = "Because RAID protects you against one and only one specific thing: disk failures."
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weight = 2
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type = "post"
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Having a number of disks in RAID may _seem_ like a backup, especially if you're using a mirror mode. But this is *wrong*!
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RAID protects you against one and only one thing: a disk failure. It does not protect you against any of the following things:
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1. Multiple disk failures beyond the RAID level chosen (e.g. both disks in a mirror, or 3 disks in a RAID-6).
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2. Failure of the RAID controller itself (especially when using hardware RAID), the computer itself, or the environment (a flood, or fire, perhaps).
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3. Data corruption on-disk (except for ZFS, and especially for BTRFS) from cosmic rays, or minor hardware or firmware failures.
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4. File corruption from bad writes or bit rot (except for ZFS), including whole-volume corruption from administrative mistakes (e.g. =mkfs= on an existing filesystem).
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5. Malicious or accidental deletion or modification of data by yourself or another party, including viruses.
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The adage is simple: "RAID replicates _everything_, even the stuff you don't want, like the deletion of that file you needed."
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For these reasons and more, RAID IS NOT A BACKUP!
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