[linux-lvm] Why is my LVM Mirror performance so bad?

[Brassow Jonathan]

On Sep 27, 2014, at 12:42 PM, Errol Neal 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 at 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 at 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 at 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 at 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 at 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?

Is the performance also degraded in this way when using single machine (i.e. not cluster)?

 brassow