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(LONG) Delay when writing to ext4 LVM after boot



(I previously asked this question in the LVM list, and they suggested I ask here.)

I have a large LV, about 6.5T, consisting of 4 physical drives of various sizes. The LV is formatted as ext4. There is no raid  involved (hardware of software).

After I first boot, if I try to write a large file (>~ 80M) to this LV, the write hangs for about 1minute or more, then continues on at full speed and finishes successfully. Writes of small files don't show this delay. After that first write and delay, all subsequent writes to other large files proceed at full speed.

I am currently running Fedora 17 64bit  (kernel 3.8.4-102.fc17.x86_64) but have noticed this also in previous systems (both 64 and 32bit). With smaller file systems ( < 1T ), there was a delay, but it was small, and it increased significantly as I increased the LV size.

I have run e2fsck with the -D option (before attempting a write), which made no difference. Also, fwiw,  I am mounting this with the default options. I've tried other options that were suggested to tweak ext4, but, again, no effect. This LV is also not my system (root) partition - that is on a separate physical drive.

Any ideas? Suggestions?

(I will gladly supply additional info as requested.)

TIA

ken




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