On Thu, 4 Sep 2014, ???????? wrote:
>
> hi, guys:
>
> when I read the filestore.cc, I find the ceph use crc the check the data.
> Why should check the data?
>
> In my knowledge, the disk has error-correcting code (ECC) for each
> sector. Looking at wiki: http://en.wikipedia.org/wiki/Disk_sector, "In disk
> drives, each physical sector is made up of three basic parts, the sector
> header, the data area and the error-correcting code (ECC)". So if the data
> is not correct. the disk can recovery it or return i/o error.
>
> Does anyone can explain it?
These checksums are not terribly reliable, and I think not even present on
all disks.
Note that the CRC checks in FileStore today are opportunistic and there
primarily for our QA environment; we don't recommend enabling them in
production environments right now because we're not sure what the
performance implications are.
sage
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