From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kirby Zhou" Date: Tue, 7 Sep 2010 00:23:23 +0800 Message-ID: <001901cb4ddf$d3bff6d0$7b3fe470$@com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001A_01CB4E22.E1E4BD70" Content-Language: zh-cn Subject: [linux-lvm] Does LVM-LV take system cache? Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: To: "'Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list'" , 'LVM general discussion and development' This is a multi-part message in MIME format. ------=_NextPart_000_001A_01CB4E22.E1E4BD70 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 ------=_NextPart_000_001A_01CB4E22.E1E4BD70 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

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=3D/dev/sdc = bs=3D1M of=3D/dev/null count=3D500

524288000 bytes (524 MB) copied, = 1.88267 seconds, 278 MB/s

[@djt_18_69 ~]# dd if=3D/dev/sdc = bs=3D1M of=3D/dev/null count=3D500

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=3D/dev/vgext/lvtest5 bs=3D1M of=3D/dev/null count=3D500

524288000 bytes (524 MB) copied, = 2.17848 seconds, 241 MB/s

[@djt_18_69 ~]# dd = if=3D/dev/vgext/lvtest5 bs=3D1M of=3D/dev/null count=3D500

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

 

------=_NextPart_000_001A_01CB4E22.E1E4BD70--