On 01/05/2014 12:09 PM, Chris Murphy wrote:
I haven't read anything so far indicating defrag applies to the VM container use case, rather nodatacow via xattr +C is the way to go. At least for now.
Can you elaborate on the rationale behind database or VM binaries being set nodatacow? I experimented with this*, and found no significant (to me, anyway) performance enhancement with nodatacow on - maybe 10% at best, and if I understand correctly, that implies losing the live per-block checksumming of the data that's set nodatacow, meaning you won't get automatic correction if you're on a redundant array.
All I've heard so far is "better performance" without any more detailed explanation, and if the only benefit is an added MAYBE 10%ish performance... I'd rather take the hit, personally.
* "experimented with this" == set up a Win2008R2 test VM and ran HDTunePro for several runs on binaries stored with and without nodatacow set, 5G of random and sequential read and write access per run.
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