On 10/20/2011 08:13 AM, Charles Polisher wrote:
Mon, Oct 10, 2011, Dennis Jacobfeuerborn wrote:
<snip /> > The physical numbers are consistent and what I would expect to see from the > sata drives. > The guests are minimal centos 6 installations so after booting they have > virtually no processes running that could influence the benchmarks in any > significant way. The hosts system is installed on /dev/sda so /dev/sd(b|c) > are not influenced by the host system either. > The entire setup is arranged to make benchmarking mostly reliable. > If there were minor temporary fluctuations I would blame some external > process but differences of almost 100% that are consistent for the lifetime > of the virtual machine do not fit such a scenario.
Hi Dennis,
Did you figure this out?
I'd suggest running something like smartctl -t long to rule out underlying issues with a drive.
But that's what puzzles me. On the host side both drives behave exactly identical and as expected. It's only in the guests where things get strange. I now have created a second disk /dev/vdb with an image on the second drive in my first guest so that it has disk from both physical drives that I can test in the same VM. These are the results:
seekmark: /dev/vda: 130 seeks/s /dev/vdb: 9615 seeks/s
hdparm -t: /dev/vda: 95 MB/s /dev/vdb: 1691 MB/s
Running iostat shows no I/O activity when running the tests for /dev/vdb which explains the insane numbers. The question is why I get such different results when both devices are defined exactly the same way?
In the guest the drive are running using virtio with type=raw and cache=none. On the host the backing filesystems look exactly the same:
[dennis@nexus ~]$ cat /proc/mounts|grep backup /dev/sdb3 /mnt/backup01 ext4 rw,seclabel,relatime,user_xattr,acl,barrier=1,data=ordered 0 0 /dev/sdc3 /mnt/backup02 ext4 rw,seclabel,relatime,user_xattr,acl,barrier=1,data=ordered 0 0
The drives are identical in every possible way:
[dennis@nexus ~]$ sudo hdparm -i /dev/sdb
/dev/sdb:
Model=SAMSUNG HD103SJ, FwRev=1AJ100E5, SerialNo=S246J9JB801028 Config={ Fixed } RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4 BuffType=unknown, BuffSize=unknown, MaxMultSect=16, MultSect=16 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=1953525168 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120} PIO modes: pio0 pio1 pio2 pio3 pio4 DMA modes: mdma0 mdma1 mdma2 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 AdvancedPM=yes: disabled (255) WriteCache=enabled Drive conforms to: unknown: ATA/ATAPI-0,1,2,3,4,5,6,7
* signifies the current active mode
[dennis@nexus ~]$ sudo hdparm -i /dev/sdc
/dev/sdc:
Model=SAMSUNG HD103SJ, FwRev=1AJ100E5, SerialNo=S246J9JB801029 Config={ Fixed } RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4 BuffType=unknown, BuffSize=unknown, MaxMultSect=16, MultSect=16 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=1953525168 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120} PIO modes: pio0 pio1 pio2 pio3 pio4 DMA modes: mdma0 mdma1 mdma2 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 AdvancedPM=yes: disabled (255) WriteCache=enabled Drive conforms to: unknown: ATA/ATAPI-0,1,2,3,4,5,6,7
* signifies the current active mode
Regards, Dennis