Performance degradation on thin logical volumes

Issue

• Performance degradation is seen on thin logical volumes when compared to standard logical volumes. This issue is characterized by a consistently lower throughput for reads and writes on the thin LV, along with roughly double the time spent in sys per dd command.

[root@host~]# lvs -a -o +devices
  LV                 VG      Attr       LSize   Pool       Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices                    
  [lvol0_pmspare]    testvg  ewi-------   4.00m                                                           /dev/mapper/mpathbp1(300)  
  mythinpool         testvg  twi-aot---   1.17g                   0.01   1.07                             mythinpool_tdata(0)        
  [mythinpool_tdata] testvg  Twi-ao----   1.17g                                                           /dev/mapper/mpathbp1(301)  
  [mythinpool_tmeta] testvg  ewi-ao----   4.00m                                                           /dev/mapper/mpathbp1(601)  
  testlv             testvg  -wi-a-----   1.17g                                                           /dev/mapper/mpathbp1(0)    
  thinvolume         testvg  Vwi-a-t---   1.07g mythinpool        0.01                                                                     

[root@host~]# time dd if=/dev/zero of=/dev/mapper/testvg-testlv bs=4096 count=262206 oflag=direct
262206+0 records in
262206+0 records out
1073995776 bytes (1.1 GB) copied, 95.1148 s, 11.3 MB/s

real    1m35.117s
user    0m0.147s
sys 0m4.851s

[root@host~]# time dd if=/dev/zero of=/dev/mapper/testvg-thinvolume bs=4096 count=262206 oflag=direct
262206+0 records in
262206+0 records out
1073995776 bytes (1.1 GB) copied, 103.106 s, 10.4 MB/s

real    1m43.119s
user    0m0.191s
sys 0m8.104s