Greg Freemyer wrote:
All, On the mdraid list, there was a recent thread about using raid functionality to detect / repair silent corruption. The issues brought up were that a lot of silent data corruption occurs when cables, controllers, power supplies, ram, cache, etc. goes bad. It made me think about another option for detecting silent corruption I have not seen discussed, but maybe I missed it. Aiui, the ATA spec allows for the reading of a long sector as well as the normal 512 byte sector. When you get a long sector you also get the CRC (or whatever checksum data there is on the disk that allows the drive itself to detect media errors). I don't have any idea how easy or hard it would be to do, but I would like to see the entire block subsystem enhanced to optionally allow long sector reads to be used in a "paranoid" fashion. Effectively it would be: 1) Read long sector from drive: verify CRC in kernel. This tests most everything on the i/o path. 2) maintain CRC type information in block subsystem. Verify no corruption just before handing off to userspace. This would potentially identify CPU/cache/RAM failures.
Even if the drive supports those commands the problem is the CRC/ECC data is in a vendor-specific format, so it couldn't be processed generically.
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