Re: IOPS higher than expected on randwrite, direct=1 tests

[John Cagle <jcagle@xxxxxxxxx>]

If the disk is 2TB, then your 100GB test is only using 5% of it-- thus your observed IOPS will be a lot better than expected due to short-stroking.  Right?

On Nov 10, 2010, at 11:58 AM, Sebastian Kayser <sebastian@xxxxxxxxxx> wrote:

> * Sebastian Kayser <sebastian@xxxxxxxxxx> wrote:
>> What I will do now is to export the whole 2TB of the disk (instead of
>> just 10GB) and increase size= to see whether that makes any difference
>> (hopefully). Other than that, further ideas?
> 
> Interim update. Exported the whole 2TB disk as a LUN, mkfs.ext3'd it and
> set size=100g in fio's configuration. Also set runtime=1800, re-started
> the test and could observe ~80 IOPS ... my dear heart was jumping with
> joy :)
> 
> However, a few minutes into the test, IOPS started to increase steadily
> and by now have again reached (non-bursty) regions that don't seem
> plausible for a single 7.2K SATA disk.
> 
> root@ubuntu-804-x64:~# ./fio --section=iscsi patterns.fio 
> iscsi: (g=0): rw=randwrite, bs=4K-4K/4K-4K, ioengine=sync, iodepth=1
> Starting 1 process
> iscsi: Laying out IO file(s) (1 file(s) / 102400MB)
> Jobs: 1 (f=1): [w] [48.4% done] [0K/986K /s] [0/240 iops] [eta 15m:28s] 
> 
> root@ubuntu-804-x64:~# cat patterns.fio 
> [global]
> size=100g
> runtime=1800
> direct=1
> sync=1
> overwrite=1
> 
> [iscsi]
> directory=/mnt
> rw=randwrite
> 
> root@ubuntu-804-x64:~# df -h /mnt
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sdb1             1.9T  101G  1.7T   6% /mnt
> 
> Well, I am so used to see less IOPS than hoped for ... but obviously not
> this time and it's driving me crazy :) Any further thoughts greatly
> appreciated.
> 
> Sebastian
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