Slow file access

[Rick Stevens]

On Tue, 2007-12-04 at 15:53 -0800, Tod Merley wrote:
> 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"?
> >
> >
> >
> > --
> >
> > fedora-list mailing list
> > fedora-list at redhat.com
> > To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list
> >
> 
> 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

Interesting stuff on SMART itself at

	http://www.linuxjournal.com/article/6983

At least you'll know how to read those values.
----------------------------------------------------------------------
- Rick Stevens, Principal Engineer             rstevens at internap.com -
- CDN Systems, Internap, Inc.                http://www.internap.com -
-                                                                    -
-            The gene pool could use a little chlorine.              -
----------------------------------------------------------------------