Monday, 14 November 2011

Data loss on JBODs

After a disasterous data loss coused by the raid system I have changed all to JBOD assuming that 1/8 data loss is more acceptable than a full disaster.

Wrong. If you have eight drives in JBOD, and one of them dies, there are several options:
  • On NTFS filesystem, if first drive dies, the entire array is lost. If any other drive dies, 7/8th of the data is lost.

  • On ext-whatever, you can salvage an unspecified amount of data because the superblocks are distributed more-or-less evenly across the volume. However, everything in disk groups which span across two disks is likely lost. So you can theoretically approach "1/8th of the data lost", but that involves using some data recovery software and is far from easy.

If you want to be sure that the loss is limited to 1/8th of data in eight-disk configuration, forget JBOD and create eight separate volumes instead.

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