Re: RAID-10 initial sync is CPU-limited

[Jan Kasprzak <kas@fi.muni.cz>]

John Robinson wrote:
: >	Yes, I am aware of this. A single disk is able to do about
: >147 MB/s according to hdparm -t. However (a big "however"),
: >my usage pattern rarely issues big/sequential requests, and for more
: >random load the total throughput generated by all disks will be
: >much lower and the disks themselves become the bottleneck.
: 
: Sure, but doing a resync does require huge sequential reads and writes.

	Yes, but it does not need to be further throttled by using
a single CPU core.

: >Anyway, my SAS controller is connected by PCIe 2.0 x8, which equals
: >to (if I read Wikipedia correctly :-) 32 Gbit/s, i.e. 2 GByte/s.
: >So PCIe is not a bottleneck here. SAS is, and I am aware of that.
: 
: Which is why the the md kernel threads appear to be using 100% of CPU, 
: they're blocked waiting for I/O. (And possibly RAM, per my other reply 
: to this thread.)

	I don't think those threads are busy-waiting for I/O.
And other type of waiting does not appear as using 100% CPU.

	Sincerely,

-Yenya

-- 
| Jan "Yenya" Kasprzak  <kas at {fi.muni.cz - work | yenya.net - private}> |
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