Tar (but not cp) is incredible slow on certain dirs; request for comments/solution ideas/clues.

Dr. Michael Weller (eowmob@exp-math.uni-essen.de)
Thu, 21 Jan 1999 11:20:54 +0100 (MEZ)

Hi people,

I've the following weird behaviour on a Compaq Proliant, 1Gig phys ram,
Smart2 Compaq raid adapter with 6 disk Raid 5 array, 2 Xeon CPU's.

I tried using both CPU's or only one (disabling it from the bios). I tried
kernel 2.0.36 and 2.2.0pre7 (always with SMP compiled in (even when only 1
CPU was used)). I also tried restricting the kernel memory to 64MB (side
note: It appeared (!) to be a little faster with this setting, I assume
handling/searching 1Gig of disk caches is much too slow. If it is not
possible to speed the handling of cache memory up, maybe it is smarter to
allow to set the kernel to use a maximum of n MB of buffer/caches memory.

Anyway, effect under all those kernels/# of CPU's is as follows: I try to
backup / (whole linux is in one partition) to another disk, file on same
disk, or even /dev/null (it doesn't matter). It runs nicely. But when it
comes to /usr/src/linux-2.2.0pre7 where the 2.2.0pre7 sources are, it
slows down to a crawl. That means it backs up one of these really tiny *.c
and *.h files there per 1 or 2 seconds. Basically, it is impossible to
back this dir up in any reasonable time.

I used tar -l as to exclude /proc and /mnt where the destination disk was
mounted. Still, even 'tar -cvf/dev/null /usr/src' showed the exact same
behaviour although it slowed down faster as it came faster to
/usr/src/linux-2.2.0pre7 .

During the slow down, top claims system is well over 90% percent idle,
CPU time consumed by tar and general system time spent is virtually zero
(1 or 2 %). Tar is not locked in an uninterruptible sleep waiting for a
device ('D') nor is there any apparent high disk activity (it just gets
these tiny files every few seconds).

To make things even more weird, cp -rv /usr/src /mnt works like a greased
weasel. So, a simple filesystem/disk cache/dname cache/disk device or
driver issue can IMHO be excluded.

Now, honestly, this is the very first time with linux I really have no
clue what's going on. Therefore any comments and ideas are appreciated.


P.S. Files and disks are currently moved around a bit more on this
machine. I'll see if the same holds when /usr/src/linux-2.2.0pre7 was
moved to another partition.


Michael Weller: eowmob@exp-math.uni-essen.de, eowmob@ms.exp-math.uni-essen.de, or even mat42b@spi.power.uni-essen.de. If you encounter an eowmob account on any machine in the net, it's very likely it's me.

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