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From: "Kirby Zhou" <kirbyzhou@sohu-rd.com>
To: "'Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list'"
	<rhelv5-list@redhat.com>,
	'LVM general discussion and development' <linux-lvm@redhat.com>
Subject: [linux-lvm] Does LVM-LV take system cache?
Date: Tue, 7 Sep 2010 00:23:23 +0800	[thread overview]
Message-ID: <001901cb4ddf$d3bff6d0$7b3fe470$@com> (raw)

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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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             reply	other threads:[~2010-09-06 16:23 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-09-06 16:23 Kirby Zhou [this message]
2010-09-06 20:16 ` [linux-lvm] Does LVM-LV take system cache? Sure Lars Ellenberg
2010-09-07  5:49   ` Kirby Zhou

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