On 10/12/2014 1:04 PM, Digimer wrote:
If it's only 1 Gbps, then the maximum sustainable write speed is ~120
MB/sec (at most; the slower of network or disk determines the max
speed). You want the sync rate to be ~30% of maximum speed, or else
you will choke out the apps using the DRBD resource and cause them to
suffer a huge performance hit. App performance is (max write - sync
rate) when a background sync is performed. This is why the default
speed is very low.
In your case, you've set the sync rate way above what is possible, and
I've seen this dramatically hurt performance and even full-on stall
the sync operation. I would set this to '40M' at most.
verify apparently uses this same speed to limit how fast it runs...
since its doing checksums on each side, its not actually transferring
any data across the network, hence why I boosted it to 200M (that left
the node that initiated the verify with one process at 90% CPU, whihc I
figure is as fast as it can go)... as I said, I've set it back to 50M
now that the verify completed.
btw, originally I had the verify-alg as sha1... my xeon X5650 2.7Ghz
could only verify about 23MB/sec. setting it to crc32c sped up to
180-200MB/sec, which is more reasonable considering this is a 16TB
volume built from 2 8x3TB drive raid6's striped together, behind a lsi
9261-8i megaraid sas2 card with 512MB BBU cache.
--
john r pierce 37N 122W
somewhere on the middle of the left coast
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