Because it is LVM! :)
On Sat, Sep 27, 2014 at 10:42 PM, Errol Neal <eneal@businessgrade.com> wrote:
Hi There. Hoping to get some clarity on some performance woes in a little testing environment that I've setup.
I am experimenting with LVM mirrors on a CentOS 6.5 cluster.
I have two VMs running on ESX5.5 that are sharing two RDM luns from an SRP target server running SCST.
Performance however seems to take a huge hit compared to a vanilla volume
[root@scst1 ~]# vgs
VG #PV #LV #SN Attr VSize VFree
hadata 2 5 0 wz--nc 999.99g 149.99g
vg_scst1 1 2 0 wz--n- 39.51g 0
[root@scst1 ~]# lvs -a -o +devices
LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert Devices
mirror1 hadata mwi-a-m--- 100.00g 100.00 mirror1_mimage_0(0),mirror1_mimage_1(0)
[mirror1_mimage_0] hadata iwi-aom--- 100.00g /dev/sdb1(0)
[mirror1_mimage_1] hadata iwi-aom--- 100.00g /dev/sdc1(0)
mirror2 hadata mwi-a-m--- 100.00g 100.00 mirror2_mimage_0(0),mirror2_mimage_1(0)
[mirror2_mimage_0] hadata iwi-aom--- 100.00g /dev/sdb1(25600)
[mirror2_mimage_1] hadata iwi-aom--- 100.00g /dev/sdc1(25600)
mirror3 hadata mwi-a-m--- 100.00g 100.00 mirror3_mimage_0(0),mirror3_mimage_1(0)
[mirror3_mimage_0] hadata iwi-aom--- 100.00g /dev/sdb1(51200)
[mirror3_mimage_1] hadata iwi-aom--- 100.00g /dev/sdc1(51200)
mirror4 hadata mwi-a-m--- 100.00g 100.00 mirror4_mimage_0(0),mirror4_mimage_1(0)
[mirror4_mimage_0] hadata iwi-aom--- 100.00g /dev/sdb1(76800)
[mirror4_mimage_1] hadata iwi-aom--- 100.00g /dev/sdc1(76800)
test hadata -wi-a----- 50.00g /dev/sdb1(102400)
lv_root vg_scst1 -wi-ao---- 31.65g /dev/sda2(0)
lv_swap vg_scst1 -wi-ao---- 7.86g /dev/sda2(8102)
[root@scst1 ~]# dd if=/dev/sdb1 of=/dev/null bs=1M count=20000
20000+0 records in
20000+0 records out
20971520000 bytes (21 GB) copied, 41.0031 s, 511 MB/s
[root@scst1 ~]# dd if=/dev/hadata/test of=/dev/null bs=1M count=20000
20000+0 records in
20000+0 records out
20971520000 bytes (21 GB) copied, 44.344 s, 473 MB/s
[root@scst1 ~]# dd if=/dev/hadata/mirror1 of=/dev/null bs=1M count=20000
20000+0 records in
20000+0 records out
20971520000 bytes (21 GB) copied, 365.685 s, 57.3 MB/s
Is this just the life of a LVM mirror and the performance here is about as good as it gets?
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