RAID Controllers Compared!

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ron.sunden

Don’t forget that latent disk errors are one of the biggest problems with RAID technology. If you are rebuilding a RAID, Unrecoverable Read Error (URE) can stop a RAID rebuild in its track, essentially making the entire RAID volume unusable.

http://www.smbitjournal.com/2012/05/when-no-redundancy-is-more-reliable/

Typical ranges for hard drives are around 1 x 10^14 bits which means that 1 out of every 10^14 bits cannot be read. This means if you have 12TBs or 12x 1TB drives your probability of encountering a URE is one (i.e. it’s going to happen). If you have 2TB drives, then all you need is 6x 2TB drives and you will encounter a URE. If you have a RAID-5 group that has seven 2TB drives and one drive fails, the RAID rebuild has to read all of the remaining disks (all six of them). At that point you are almost guaranteed that during the RAID-5 rebuild, you will hit a URE and the RAID rebuild will fail. This means you have lost all of your data.

http://www.lucidti.com/zfs-checksums-add-reliability-to-nas-storage

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