Once again I'm stumped by some performance numbers and hoping for some
insight.
Using an 8-core server, building in parallel, I'm building some code.
Using ext2 over a 5-way, (5 disk), lvm partition, I can build that code
in 35 minutes. Tests with dd on the raw disk and lvm partitions show me
that I'm getting near linear improvement from the raw stripe, even with
dd runs exceeding 10G, so I think that convinces me that my disks and
controller subsystem are capable of operating in parallel and in
concert. hdparm -t numbers seem to support what I'm seeing from dd.
Running the same build, same parallelism, over a btrfs (defaults)
partition on a single drive, I'm seeing very consistent build times
around an hour, which is reasonable. I get a little under an hour on
ext4 single disk, again, very consistently.
However, if I build a btrfs file system across the 5 disks, my build
times decline to around 1.5 - 2hrs, although there's about a 30min
variation between different runs.
If I build a btrfs file system across the 5-way lvm stripe, I get even
worse performance at around 2.5hrs per build, with about a 45min
variation between runs.
I can't explain these last two results. Any theories?
--rich
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