RE: Linux buffer cache monitoring

From: Allen, Brandon <>
Date: Fri, 25 Jul 2008 11:46:01 -0700
Message-ID: <04DDF147ED3A0D42B48A48A18D574C450CBA9779@NT15.oneneck.corp>

Thanks Hemant, but that's not exactly what I'm trying to monitor. I'm not trying to see how much of the RAM is used/free - rather, I'm basically trying to see the Linux buffer cache hit ratio, and the components that make up that ratio (logical/buffered reads & physical reads).

I'm running Orion (Oracle's I/O capacity testing tool) and it's reporting about 5000 IOPS, but that is too good to be true considering I'm only striped across 5 disks (in RAID5), I should only be able to sustain about 625 IOPS (125 x 5, as long as they're 100% reads, which is what I'm testing with Orion). According to sar and iostat, I'm only doing about 250 IOPS and my understanding is that those are physical reads from the OS perspective (I know they might still be cached by the disk, controller, array cache, etc. in the backend). So, my guess is that the other 4500 IOPS are being done in the Linux buffer cache, but I'd like to see something to confirm that. I've got 8GB of RAM on this box and I'm testing Orion with a 64GB file, so I don't see how it could be satisfying so much of its I/O from cache.


-----Original Message-----

From: Hemant K Chitale []

I gave up trying to monitor this !

See nux.html

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-- Received on Fri Jul 25 2008 - 13:46:01 CDT

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