Eric Sandeen writes:
> Talking w/ someone who had a raid6 of 15 drives on an areca
> controller, he wondered why he could only get 300MB/s or so
> out of a streaming buffered write to xfs like so:
> dd if=/dev/zero of=/mnt/storage/10gbfile bs=128k count=81920
> 10737418240 bytes (11 GB) copied, 34.294 s, 313 MB/s
> when the same write directly to the device was going closer
> to 700MB/s...
> With the following change things get moving again for xfs:
> dd if=/dev/zero of=/mnt/storage/10gbfile bs=128k count=81920
> 10737418240 bytes (11 GB) copied, 16.2938 s, 659 MB/s
> Chris had sent out something similar at Christoph's suggestion,
> and Christoph reminded me of it, and I tested it a variant of
> it, and it seems to help shockingly well.
> Feels like a bandaid though; thoughts? Other tests to do?
If the nr_to_write calculation really yields a value that is too
small, shouldn't it be fixed elsewhere?
Otherwise it might make sense to make the fudge factor tunable.
> +
> + /*
> + * VM calculation for nr_to_write seems off. Bump it way
> + * up, this gets simple streaming writes zippy again.
> + */
> + wbc->nr_to_write *= 4;
> +
--
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