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Re: RAID-1 and disk I/O



On 7/18/21 2:16 AM, Reco wrote:
	Hi.

On Sat, Jul 17, 2021 at 02:03:15PM -0700, David Christensen wrote:
But much more noticable is the difference of data reads of the two
disks, i.e. 55 GB and 27 GB, i.e. roughly twice as much data is read
from /dev/sdb compared to /dev/sda.  Trying to figure out the reason
for this, dmesg didn't give me anything

Getting meaningful information from system monitoring tools is
non-trivial.  Perhaps 'iostat 600' concurrent with a run of bonnie++.
Or, 'iostat 3600 24' during normal operations.  Or, 'iostat' dumped to
a time-stamped output file run once an hour by a cron job.

iostat belongs to sysstat package.
sysstat provides sar, which, by default, gathers every detail of the
host resource utilization and a little more once per 10 minutes.

There's little need for the kludges you're describing for one can simply
invoke "sar -pd -f /var/log/sysstat/sa...".

Reco


Yes, sar(1) looks useful.  :-)


David


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