Convert ext4 lvm to normal ext4 partition
Lamar Owen
lowen at pari.edu
Sun Nov 14 12:31:13 UTC 2010
On Saturday, November 13, 2010 08:59:48 pm Dean S. Messing wrote:
> Regarding your disk speed tests with hdparm,
> you may want to look at the "--direct" switch.
Oh, I like those numbers:
[root at migration ~]# hdparm -t --direct /dev/sdb3
/dev/sdb3:
Timing O_DIRECT disk reads: 2054 MB in 3.02 seconds = 679.13 MB/sec
[root at migration ~]# hdparm -t --direct /dev/bench2/7g
/dev/bench2/7g:
Timing O_DIRECT disk reads: 2052 MB in 3.00 seconds = 683.36 MB/sec
[root at migration ~]#
There's hardware cache (about 4GB) involved in the array controller that I'm just not able to bypass. Although I'm going to admit that those numbers seem fishy...
And I do know why they look fishy. There's another cache involved. But I can't reproduce with /dev/sda on that box, and /dev/sda is on the same array, it's on the same HBA, and, while it's on a different LUN, it's on the same RAID group on the array:
[root at migration ~]# hdparm -t --direct /dev/sda
/dev/sda:
Timing O_DIRECT disk reads: 994 MB in 3.00 seconds = 331.18 MB/sec
[root at migration ~]#
Which is more in line with 4G/s FC performance. I'll have to dig into that anomaly.
Now, on my development F14 box hooked up to the same array, just a different LUN, and a 32-bit machine (dual Xeon 2.8, 4GB RAM), and using a 2G/s FC HBA (which will impact, and probably bottleneck, performance):
[root at www ~]# hdparm -t --direct /dev/sdw
/dev/sdw:
Timing O_DIRECT disk reads: 534 MB in 3.01 seconds = 177.46 MB/sec
[root at www ~]#
On another CentOS 5 box (dual 3.4GHz Xeon's, 2GB RAM, x86_64), hooked up to a different array with 4G FC:
[root at backup670 ~]# hdparm -t --direct /dev/sdad
/dev/sdad:
Timing O_DIRECT disk reads: 864 MB in 3.00 seconds = 287.87 MB/sec
[root at backup670 ~]#
(yeah, /dev/sdad, that's not a typo)
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