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Re: [Xen-users] IO is a big difference between the "file" and "phy"

On Wed, Jun 13, 2012 at 3:17 PM, ÐÑÑÐÐÐ ÐÐÑÐÐÐÐ <ufaweb@xxxxxxxxx> wrote:

>> - how large is your test size, relative to dom0 memory
> test size = 2 GByte, memory in dom0 = 2GByte

the image will be cached in dom0 memory, making your test invalid. You
need at least a dataset size of twice ram size to make sure caching is
not a factor.

>> - is the test I/O random or sequential
> sequential

It's kinda useless these days to do sequential testing, since most
loads (e.g. db, web server) will be random i/o. The exception is that
if you're writing/reading large, streamed video files or image (e.g.
downloading ISO/vm image).

>> - does the test use sync/direct I/O
> direct

Do you know what direct I/O is?
IIRC by default dd does not use direct or sync, so your test will be buffered.

Try fio. You can tell it to do random or sequential, sync or buffered,
specificy data size, etc.

>> Don't use file:/
> ok, it remains only to solve the problem of slow speed when using phy:/ :)

Your throughput looks normal for raid5/6. Anything above that would
mean cache comes into play.

Now if you're using striped raid 10, the story might be different.


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