Re: mkfs options for a 16x hw raid5 and xfs (mostly large files)

["Bryan J. Smith" <b.j.smith@ieee.org>]

Justin Piszcz <jpiszcz@lucidpixels.com> wrote:
> I have a question, when I use multiple writer threads (2 or 3) I
> see 550-600 MiB/s write speed (vmstat) but when using only 1
thread,
> ~420-430 MiB/s...

It's called scheduling buffer flushes, as well as the buffering
itself.

> Also without tweaking, SW RAID is very slow (180-200
> MiB/s) using the same disks.

But how much of that tweaking is actually just buffering?
That's a continued theme (and issue).

Unless you can force completely synchronous writes, you honestly
don't know.  Using a larger size than memory is not anywhere near the
same.

Plus it makes software RAID utterly n/a in comparison to hardware
RAID, where the driver is waiting until the commit to actual NVRAM or
disc is complete.


-- 
Bryan J. Smith   Professional, Technical Annoyance
b.j.smith@ieee.org    http://thebs413.blogspot.com
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