On 13/07/16 05:09, Matt Garman wrote:
We have a system with a 24-disk raid6 array, using 2TB SSDs. We use this system in a workload that is 99.9% read-only (a few small writes/day, versus countless reads). This system is an NFS server for about 50 compute nodes that continually read its data.
Perhaps naively, I would expect that second-to-last line: [ 6.499773] raid6: using algorithm avx2x4 gen() (8648 MB/s) to indicate what kind of throughput I could expect in a degraded state, but clearly that is not right---or I have something misconfigured. So in other words, what does that gen() 8648 MB/s metric mean in terms of real-world throughput? Is there a way I can "convert" that number to expected throughput of a degraded array?
I can't help you with the throughput calculation, but 24 disks would imply you are striped across 22 disks.
With a reconstruct read, you of course have to read an entire stripe from all present disks to reconstruct that sector. So I would assume your machine IO to go through the roof, in addition to whatever calculations are required to actually do the reconstruction.
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