[Lustre-discuss] lustre client /proc cached reads

[John Parhizgari]

After doing a few experimental read tests while examining 
/proc/fs/lustre/osc/OSTID/stats on the lustre client:

It seems to be that the 7th column of the stats file, on the ost_read 
line, represents the total bytes read for all the RPC calls involving 
reading from that OST up until now (2773483520 in the example below).
ost_read                  91655 samples [usec] 4096 1048576 2773483520 
1759238200229888

Is this an accurate description of ost_read?

If so, does it make sense to use information to track and analyze the 
true read stats against OSTs and filesystems (since the llite stats 
includes client-cached data reads)? And then also similarly for 
ost_write, since we want essentially Lustre's network activity to the 
filesystem; if the above holds this will be representative of how much 
data is really being transferred to/from the lustre filesystems for each 
client.

John Parhizgari wrote:
> Simply, I would like to be able to access lustre client data statistics 
> for each filesystem that excludes statistics for cached reads.
>
> It is my understanding that for the lustre client (at least on version 
> 1.6.4.2) the /proc lustre stats for the client for each fs 
> (/proc/fs/lustre/llite/FSNAME/stats) report the total number of bytes 
> read (reported in the line read_bytes), and that this number also 
> includes the total number of bytes read using client-cached data.
>
> First of all, is my understanding correct for this version of lustre? 
> And does this apply also for newer versions?
>
> It has been suggested to subtract the lustre IO from the network IO to 
> get this data, but this is only applicable if the network is dedicated 
> to Lustre IO, which is not the case.
>
> For the moment it seems only the number of cached reads are being 
> reported in /proc, and not the actual sizes, so this -seems- difficult 
> or impossible.
>
> Is there another way (perhaps even in a newer version of lustre) to find 
> the true read rate for the lustre client that excludes cached reads?
>
> --
> John Parhizgari
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