* [linux-lvm] Does LVM-LV take system cache?
@ 2010-09-06 16:23 Kirby Zhou
2010-09-06 20:16 ` [linux-lvm] Does LVM-LV take system cache? Sure Lars Ellenberg
0 siblings, 1 reply; 3+ messages in thread
From: Kirby Zhou @ 2010-09-06 16:23 UTC (permalink / raw)
To: 'Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list',
'LVM general discussion and development'
[-- Attachment #1: Type: text/plain, Size: 909 bytes --]
Does LVM-LV take system cache?
In my test, it does not take system cache on a RHEL5 box, is it a bug or a
feature?
Test1, run dd with raw block device, it seems system cache can boost up
reread operation.
[@djt_18_69 ~]# dd if=/dev/sdc bs=1M of=/dev/null count=500
524288000 bytes (524 MB) copied, 1.88267 seconds, 278 MB/s
[@djt_18_69 ~]# dd if=/dev/sdc bs=1M of=/dev/null count=500
524288000 bytes (524 MB) copied, 0.13445 seconds, 3.9 GB/s
Test2, run dd with lv, it seems system cache CAN NOT boost up reread
operation.
[@djt_18_69 ~]# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
524288000 bytes (524 MB) copied, 2.17848 seconds, 241 MB/s
[@djt_18_69 ~]# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
524288000 bytes (524 MB) copied, 2.17451 seconds, 241 MB/s
Both 2.6.18-164.15.1.el5 and 2.6.18-194.el5 do the same behavior.
Regards
Kirby Zhou
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [linux-lvm] Does LVM-LV take system cache? Sure.
2010-09-06 16:23 [linux-lvm] Does LVM-LV take system cache? Kirby Zhou
@ 2010-09-06 20:16 ` Lars Ellenberg
2010-09-07 5:49 ` Kirby Zhou
0 siblings, 1 reply; 3+ messages in thread
From: Lars Ellenberg @ 2010-09-06 20:16 UTC (permalink / raw)
To: linux-lvm
On Tue, Sep 07, 2010 at 12:23:23AM +0800, Kirby Zhou wrote:
> Does LVM-LV take system cache?
>
> In my test, it does not take system cache on a RHEL5 box, is it a bug or a
> feature?
>
> Test1, run dd with raw block device, it seems system cache can boost up
> reread operation.
>
> [@djt_18_69 ~]# dd if=/dev/sdc bs=1M of=/dev/null count=500
> 524288000 bytes (524 MB) copied, 1.88267 seconds, 278 MB/s
> [@djt_18_69 ~]# dd if=/dev/sdc bs=1M of=/dev/null count=500
> 524288000 bytes (524 MB) copied, 0.13445 seconds, 3.9 GB/s
>
>
> Test2, run dd with lv, it seems system cache CAN NOT boost up reread
> operation.
>
> [@djt_18_69 ~]# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
> 524288000 bytes (524 MB) copied, 2.17848 seconds, 241 MB/s
> [@djt_18_69 ~]# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
> 524288000 bytes (524 MB) copied, 2.17451 seconds, 241 MB/s
>
> Both 2.6.18-164.15.1.el5 and 2.6.18-194.el5 do the same behavior.
The last close() on a block device releases its cache.
As for sdc dd is most likely not the exclusive user at that time
(any mounts or other references on sdc itself, or its partitions,
count), dd's close() does not have this effect there.
Try this:
# sleep 3600 < /dev/vgext/lvtest5 & sleep_pid=$!
# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
# kill $sleep_pid
# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
Lars
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [linux-lvm] Does LVM-LV take system cache? Sure.
2010-09-06 20:16 ` [linux-lvm] Does LVM-LV take system cache? Sure Lars Ellenberg
@ 2010-09-07 5:49 ` Kirby Zhou
0 siblings, 0 replies; 3+ messages in thread
From: Kirby Zhou @ 2010-09-07 5:49 UTC (permalink / raw)
To: 'LVM general discussion and development'
Thanks very much,
the fact is actually what you said.
Regards,
Kirby Zhou
from SOHU-RD +86-10-6272-8261
-----Original Message-----
From: linux-lvm-bounces@redhat.com [mailto:linux-lvm-bounces@redhat.com] On
Behalf Of Lars Ellenberg
Sent: Tuesday, September 07, 2010 4:17 AM
To: linux-lvm@redhat.com
Subject: Re: [linux-lvm] Does LVM-LV take system cache? Sure.
On Tue, Sep 07, 2010 at 12:23:23AM +0800, Kirby Zhou wrote:
> Does LVM-LV take system cache?
>
> In my test, it does not take system cache on a RHEL5 box, is it a bug or a
> feature?
>
> Test1, run dd with raw block device, it seems system cache can boost up
> reread operation.
>
> [@djt_18_69 ~]# dd if=/dev/sdc bs=1M of=/dev/null count=500
> 524288000 bytes (524 MB) copied, 1.88267 seconds, 278 MB/s
> [@djt_18_69 ~]# dd if=/dev/sdc bs=1M of=/dev/null count=500
> 524288000 bytes (524 MB) copied, 0.13445 seconds, 3.9 GB/s
>
>
> Test2, run dd with lv, it seems system cache CAN NOT boost up reread
> operation.
>
> [@djt_18_69 ~]# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
> 524288000 bytes (524 MB) copied, 2.17848 seconds, 241 MB/s
> [@djt_18_69 ~]# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
> 524288000 bytes (524 MB) copied, 2.17451 seconds, 241 MB/s
>
> Both 2.6.18-164.15.1.el5 and 2.6.18-194.el5 do the same behavior.
The last close() on a block device releases its cache.
As for sdc dd is most likely not the exclusive user at that time
(any mounts or other references on sdc itself, or its partitions,
count), dd's close() does not have this effect there.
Try this:
# sleep 3600 < /dev/vgext/lvtest5 & sleep_pid=$!
# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
# kill $sleep_pid
# dd if=/dev/vgext/lvtest5 bs=1M of=/dev/null count=500
Lars
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