[ceph-users] Ceph Bluestore : Deep Scrubbing vs Checksums

Ronny Aasen ronny+ceph-users at aasen.cx
Sun Nov 25 10:40:31 PST 2018

On 22.11.2018 17:06, Eddy Castillon wrote:
> Hello dear ceph users:
> We are running a ceph cluster with Luminous (BlueStore). As you may 
> know this new  ceph version has a new feature called "Checksums".  I 
> would like to ask if this feature replace to deep-scrub. In our 
> cluster, we run deep-scrub ever month however the impact in the 
> performance is high.
> Source:  ceph's documentation:
> Checksums
> BlueStore calculates, stores, and verifies checksums for all data and 
> metadata it stores. Any time data is read off of disk, a checksum is 
> used to verify the data is correct before it is exposed to any other 
> part of the system (or the user).

checksum's and deep-scrub do different things. and you want to keep 
doing both.

checksum helps in determining if the data is OK or not, when reading it 
off the disk.

if you have data sitting idle on a drive, it can become unreadable due 
to bad blocks over time. if the data is never read you can end up in a 
situation where all the objects replicas have become unreadable.

deep-scrub periodically reads the data on the drive to verify it is 
still readable and correct, (checking with other replicas, and checksums)

you can schedule the deep-scrub to run on non-peek hours.

kind regards
Ronny Aasen

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