Hi,
I see some unusual block allocations on my OSTs, and I was wondering if
someone could explain to my why, and help me to fix a performance
problem.
In order to track down a performance issue, I ran the following test:
- I reformatted my OSTS (I have 4 OSTs).
- I created a 10G file on each OST.
- I ran dumpe2fs to see if I had some unusual fragmentation going on.
dumpe2fs shows the free blocks per group. There are 25900 groups on
each OST (each OST is about 3.5 T big).
On my fastest OSTs, the allocated blocks are from groups 6864 - 6950. I
would have thought that blocks would be allocated from group 0.
On the slowest OSTs, the block are allocated from groups 24053 - 24138,
which is near the end of my RAID Array (and presumably, near the end of
my disks!)
The other OSTs allocate from other groups.
This leads me to several questions:
1. Why does each OST allocate from different locations?
2. What subroutine in the code controls this?
3. Is there a way to control this, to improve my performance?
Thanks.
-Roger
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