Slow file access

[Konstantin Svist]

Here's the situation:

I have some large mysql db files on my main partition. For some strange 
reason, some of these files are very slow to be read off the disk: 
~3MB/s (I'm SCPing them to another machine). File size doesn't seem to 
be relevant (other files of approximately same size are being 
transferred at ~20MB/s), and the speed is not the same throughout the file.

My first thought was that the file got very fragmented (I'm fairly sure 
that the partition was filled up to [almost] 100% at some point). 
Usually, that can be remedied by copying the file to another location on 
the same partition.. or rather, that's what would fix fragmented files 
on NTFS. When I tried that, the read speed of the new file was better by 
a small amount (up to ~5MB/s) - although that could be because the file 
was still in the memory cache.

I also thought that HD might be nearing the end of its useful lifetime 
(and has to re-read the sectors, causing the horrible slowdown), but I 
didn't notice any alerts from SMART (including the output of smartctl 
-a, anyway)

The partition is ~60-70% full, type ext3 with noatime enabled.
Speed tests were performed by "scp myfile localhost:/dev/null"



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