On Mar 20, 2014, at 8:36 AM, Bernd Schubert [off-list ref] wrote:

On 03/20/2014 04:35 PM, Bernd Schubert wrote:

quoted

quoted

Yes.  The article gives 16384 and 32768 as examples for
stripe_cache_size.  Such high values tend to reduce throughput instead
of increasing it.  Never use a value above 2048 with rust, and 1024 is
usually optimal for 7.2K drives.  Only go 4096 or higher with SSDs.  In
addition, high values eat huge amounts of memory.  The formula is:

Why should the stripe-cache size differ between SSDs and rotating disks?
Did you ever try to figure out yourself why it got slower with higher
values? I profiled that in the past and it was a CPU/memory limitation -
the md thread went to 100%, searching for stripe-heads.

Sorry, I forgot to write 'cpu usage', so it went to 100% cpu usage.

quoted

So I really wonder how you got the impression that the stripe cache size
should have different values for differnt kinds of drives.


Cheers,
Bernd

--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

The hash chains for the stripe cache become long if you increase the stripe cache.  There are only 256
hash buckets.  With 32K stripe cache entries, the average length of a hash chain will be 128 and that will
increase contention for the lock protection the chain.

-eivind