Comparison of local storage performance

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Hierarchy: VMmanager KVM -> Cluster configuration
VMmanager Cloud -> Cluster configuration

VMmanager supoorts a number of local and network storage. Local: LVM, DIR (RAW, QCoW2 formats).

To compare performance of local storages we run a test.

Methods

  • We used the fio.
  • We measured iops
  • Reads and writes were tested separately.
  • The following parameters were used for testing:
    • Read:

[readtest]
blocksize=128k
filename=/dev/vdb
rw=randread
direct=1
buffered=0
ioengine=libaio
iodepth=16

  • Write:

 [writetest]
 blocksize=128k
 size=100%
 filename=/dev/vdb
 rw=randwrite
 direct=1
 buffered=0
 ioengine=libaio
 iodepth=16

Each test was run 3 times. Before each test, the disk was set to zero through the dd utility, and disk OS cache was reset ( echo 3 > /proc/sys/vm/drop_caches )

The resulting value is the average value from those we got during the test (not the arithmetic mean from 3 values, but the average value). Values differed greatly depending on the test.

The following servers were used:

  • Processor: Intel Core2Quad CPU Q6600
  • RAM: 8 Gb
  • Disk system: adaptec RAID 10, with 4 SAS disks 150 Gb each
  • ОS: CentOS-6

The fio utility was installed from the EPEL repository.

For tests we created a 50000 Mb virtual disk. The virtio driver was used to connect disks to virtual machines.

To test a node by one method, we used sda4 (on which both LVM and disks for virtual machines were created later) and specified the size=50G option in fio

For the other method we created the LVM volume group. 500000 MB LVM partition was created in this group the same way as for the virtual machine.

To test DIR storages with RAW and QCoW2 formats, the disk images in the form of files were located in the /vm directory of the ext4 file system.

Results

Storage type Read test result, IOPS Write test results, IOPS
Read/write on physical server 843 331
LVM-partition on physical server 848 559
Virtual machine on DIR (RAW) 668 545


Virtual machine on DIR (QCoW2) 621 463


Virtual machine on DIR (QCoW2) + snapshot 615 56
Virtual machine on LVM 854 557

Conclusion

The fastest storage is LVM.

RAW storage is the easiest to configure for any incidents.

The advantage of QCoW2 is support for snapshots, however, snapshots significantly slow down record (until all the block are overwritten).