Software RAID & Filesystem Cache
Quoted 8 lines · Philip Molter
Mike Hardy wrote:
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The readahead is the first place I'd look though. All in all, it appears that 2.6 kernels need a great deal more I/O tuning before they can be put in production. While I like the flexibility that's available, the default settings seem to be a major negative change from 2.4. This sort of thing is just now being quantified and hopefully it gets sorted out in the next couple of releases
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My first suspicion was readahead as well, but I couldn't find any of the sysctl options to control readahead in the kernel (as there were under
I'm honestly not trying to be a smart-ass by posting this since I haven't played with these *a single bit* - however, this was what I found:
<berlin>/sys % find . | grep ahead./block/hdf/queue/read_ahead_kb./block/hdg/queue/read_ahead_kb./block/hdc/queue/read_ahead_kb./block/hda/queue/read_ahead_kb
Maybe those are the appropriate knobs to twiddle? If so, it appears they've gone per-device, and they've moved to sysfs...
-Mike
Quoted 11 lines
I'm honestly not trying to be a smart-ass by posting this since I haven't played with these *a single bit* - however, this was what I found:
<berlin>/sys % find . | grep ahead
./block/hdf/queue/read_ahead_kb./block/hdg/queue/read_ahead_kb./block/hdc/queue/read_ahead_kb./block/hda/queue/read_ahead_kbMaybe those are the appropriate knobs to twiddle? If so, it appears they've gone per-device, and they've moved to sysfs...
Thanks! Maybe that's why I couldn't find it. I was looking through sysctl settings, which only run through /proc (I guess). I keep forgetting /sys exists now.
Philip
Quoted 5 lines
<berlin>/sys % find . | grep ahead
./block/hdf/queue/read_ahead_kb./block/hdg/queue/read_ahead_kb./block/hdc/queue/read_ahead_kb./block/hda/queue/read_ahead_kb
Yeah, these definitely have no effect on how much is being read from the disks. There is a direct correlation, though, between the chunk size on the raid0 portion of the raid10 and the amount of data that is read. If you increase the chunk size, you increase not just the number of bytes read from the disks.
There's something seriously messed up with software RAID10. It's practically unusable for high-load situations where before it was perfectly fine.