>If you look at /proc/diskstats and particularly the 4th and 6th fields for
>the device that you are interested in, and then take the differences for each
>field between 'before' and 'after' running a test you will get
> - the number of IO requests
> - the number of sectors
>
>that were serviced during that time. Taking a ratio will get you the number
>of sectors per IO. Normally more is better.
Hi Neil,
are you sure the right value are the 4th and the 6th fields ? I see strange
value in them (the 4th field is bigger then the 6th while i was expecting the
contrary)
looking in the iostats.txt file (kernel documentation) i suspect the fields you
are interested are the first and the third.
In this hypothesis (1st and 3rd fields) the ratio i obtain are:
sda 84.02
sdb 113,69
md2 8,01
md2 and his meber have a very different ratio....
>It might be interesting to find out what the data offset is for your RAID1
>(mdadm --examine will tell you if there is one), and compare the
> request/sector numbers and see if they show anything.
this is the output of mdadm --examine /dev/sda3
/dev/sda3:
Magic : a92b4efc
Version : 0.90.00
UUID : d7ca6fdd:8cf9e3ed:bea46eb0:98c63a97
Creation Time : Tue Sep 23 15:49:29 2008
Raid Level : raid1
Used Dev Size : 237826176 (226.81 GiB 243.53 GB)
Array Size : 237826176 (226.81 GiB 243.53 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 2
Update Time : Tue Jul 27 18:07:41 2010
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Checksum : 8afc34a - correct
Events : 18156
Number Major Minor RaidDevice State
this 0 8 3 0 active sync /dev/sda3
0 0 8 3 0 active sync /dev/sda3
1 1 8 19 1 active sync /dev/sdb3
Do you have some hypothesis ?
thank you all
Marco
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
