* dm-cache warming
@ 2013-07-26 15:24 Dave Pitts
2013-07-29 10:16 ` Heinz Mauelshagen
0 siblings, 1 reply; 3+ messages in thread
From: Dave Pitts @ 2013-07-26 15:24 UTC (permalink / raw)
To: dm-devel
Hello:
I've been trying to do some performance testing for a client and can't seem to
get the dm-cache warmed. The values displayed in the "dmsetup status" command
seem too low. I've been trying to use the "raw" devices setup for the cache and
NOT use a file system or database. I've tried sequential writes/reads to the
devices (ie. dd ) and dividing up the space to be tested and do I/O over a
number of segments to try to break any sequential I/O tests. Any ideas as to
what I may doing wrong? Do I need to randomize the I/O?
System: RHEL 7.0 Alpha3, 3.9.7 kernel
Thanks in advance..
--
Dave Pitts PULLMAN: Travel and sleep in safety and comfort.
dpitts@cozx.com
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: dm-cache warming
2013-07-26 15:24 dm-cache warming Dave Pitts
@ 2013-07-29 10:16 ` Heinz Mauelshagen
2013-07-29 10:40 ` Joe Thornber
0 siblings, 1 reply; 3+ messages in thread
From: Heinz Mauelshagen @ 2013-07-29 10:16 UTC (permalink / raw)
To: dm-devel
Hi,
dm-cache is a hot-spot cache. Ie. you need multiple accesses to the same
block to get it promoted into the cache (depending on the policy plugin
btw).
If your patterns is one-time-only access type, it ain't warm the cache.
Heinz
On 07/26/2013 05:24 PM, Dave Pitts wrote:
> Hello:
>
> I've been trying to do some performance testing for a client and can't
> seem to get the dm-cache warmed. The values displayed in the "dmsetup
> status" command seem too low. I've been trying to use the "raw"
> devices setup for the cache and NOT use a file system or database.
> I've tried sequential writes/reads to the devices (ie. dd ) and
> dividing up the space to be tested and do I/O over a number of
> segments to try to break any sequential I/O tests. Any ideas as to
> what I may doing wrong? Do I need to randomize the I/O?
>
> System: RHEL 7.0 Alpha3, 3.9.7 kernel
>
> Thanks in advance..
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: dm-cache warming
2013-07-29 10:16 ` Heinz Mauelshagen
@ 2013-07-29 10:40 ` Joe Thornber
0 siblings, 0 replies; 3+ messages in thread
From: Joe Thornber @ 2013-07-29 10:40 UTC (permalink / raw)
To: device-mapper development
On Mon, Jul 29, 2013 at 12:16:11PM +0200, Heinz Mauelshagen wrote:
>
> Hi,
>
> dm-cache is a hot-spot cache. Ie. you need multiple accesses to the
> same block to get it promoted into the cache (depending on the
> policy plugin btw).
>
> If your patterns is one-time-only access type, it ain't warm the cache.
Remember there's the page cache in front of dm-cache too. You may be
accessing data many times, but not actually hitting the disk with
your requests.
- Joe
^ permalink raw reply [flat|nested] 3+ messages in thread
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