Slow file access

[Tod Merley]

On Dec 4, 2007 3:09 PM, Konstantin Svist <fry.kun at gmail.com> wrote:
> Tod Merley wrote:
> > On Dec 4, 2007 2:03 PM, Konstantin Svist <fry.kun at gmail.com> wrote:
> >
> >> 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"
> >>
> >>
> >>
> >> ----SNIP
> >
> > Hi Konstantin Svist!
> >
> > If I understand the data:
> >
> > Lots of seek errors - lots of ECC recoveries - running very warm (117
> > degrees Farenheit).  Check for cooling issues.  Low level format if
> > possible.
> >
> > Sounds kind of like the little guy has worked very hard for you the
> > last year and a half!  Yes, maybe time to change him out.
> >
> > Just some thoughts!
> >
> > Tod
> >
> >
>
> Thanks, Tod!
>
> Just now I checked the value of "195 Hardware_ECC_Recovered" - it seems
> to be increasing by a large amount every second. However, the same thing
> is happening on most of my HDs (I see that number increase by ~15-20K/s
> on the machine with the slow file, and ~45K/s on some 1-month-old SATA
> drives (those might have a different load, however).
> Is this normal? (these are all HD-intensive servers, BTW, mostly DB
> accesses)
>
>
> I also remember hearing on this list that it's not certain how to read
> some SMART values... look for thread "Fedora May Be Killing Your
> Laptop's Hard Drive?". The attribute in question was "193
> Load_Cycle_Count" but maybe the same thing applies to the other "raw data"?
>
>
>
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Hi again Konstantin Svist!

I am no expert, simply an interested party.

I did find this study, however:

http://research.google.com/archive/disk_failures.pdf

Good Reading!

Tod