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List:       linux-lvm
Subject:    Re: [linux-lvm] Trying to see a difference in performance with LVM Cache
From:       Dax Kelson <dkelson () gurulabs ! com>
Date:       2015-07-10 22:59:27
Message-ID: CAFDa5Q349Nea9whsOejG7oMVHKqt73eKuLO1svLm7uRyut2S4g () mail ! gmail ! com
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On Fri, Jul 10, 2015 at 4:53 PM, Dax Kelson <dkelson@gurulabs.com> wrote:
> My "root" LV is attached to a LVM Cache Pool that is about 900GB in size.
>
> The Origin/Slow LV can do about 560 MB/sec and the Fast/CacheLV can do
> about double that speed.


Here is the speed going directly against the Cache data LV and the OriginLV.

[root@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root@virthost03 tmp]# dd if=/dev/mapper/virthost03-CacheLV_cdata
of=/dev/null count=1 skip=30  bs=1GB
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 1.08997 s, 917 MB/s
[root@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root@virthost03 tmp]# dd if=/dev/mapper/virthost03-root_corig
of=/dev/null count=1 skip=30  bs=1GB
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 1.73674 s, 576 MB/s
[root@virthost03 tmp]#

Reading from the CacheLV is slower than even the OriginLV?!?

[root@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root@virthost03 tmp]# dd if=/dev/mapper/virthost03-root  of=/dev/null
count=1 skip=30  bs=1GB
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 6.77021 s, 148 MB/s

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