Do you have any of Performance monitoring Tooks installed? You can see
if the virtual machine cpu usage goes up when copying to LVM vs non-LVM
What is your PE size?
עופר ברוך
<offerbar...@gmai
l.com> To
Sent by: Linux [email protected]
on 390 Port cc
<[email protected]
IST.EDU> Subject
z/Linux dasd performance issue
08/04/2009
06:46 AM
Please respond to
Linux on 390 Port
<[email protected]
IST.EDU>
Hi all,
I have a big performance problem running Redhat V5.2 on system z.
The configuration looks like this:
I gave the test Linux an absolute share of 50% (limithard) so cpu won't
vary
from one test to the other (I have 1 IFL on a z9 BC machine)
Linux has 1GB of RAM – no paging from the VM side or Linux size (this is a
test guest with nothing on it).
I am using model-3 ECKD disks using Hitachi disks. No PPRC is involved. We
have 4 Ficon chpids connected to the z/VM (shared with z/OS. Ficons
utilization at about 10%).
For the problem itself…
I received bad performance reports from my dba (using oracle 10g on
z/Linux)
- a simple create table space of 300MB takes about 40 seconds…
Another test to create the same table space on a tmpfs took 2 seconds.
So, I figured that the problem is I/O related and not Oracle related…
Note: before every test I run the following commands to clear the cache:
sync; echo 3 > /proc/sys/vm/drop_chaches; sync
I then tried the following command in order to write directly to the
device:
dd if=/dev/zero of=/dev/dasd bs=4096 count=75000 (about 300M)
I receive 200-400MB per second. So far so good.
I then tried to do the following (writing to the partition):
dd if=/dev/zero of=/dev/dasd1 bs=4096 count=75000 (about 300M)
I receive 60-90MB per second.
I then tried writing to a file system:
dd if=/dev/zero of=/oracle/datafiles/big_file.txt bs=4096 count=75000
(about
300M)
I receive 10-30MB per second.
I did many more tests… writing to a file system that resides directly on
the
dasd/partition/lvm/lvm with striping etc…
All returned very bad performance.
I also tried writing to the dasd/partition on SLES and received the same
results. Very good performance writing directly to the disk very bad
performance writing to the partition.
I also tried writing to the dasd/partition on a native LPAR and received
the
same results.
Any thoughts?
Is my test case ok? Am I doing something wrong?
Is this normal behavior?
I expect z/Linux to give me great I/O performance… What's wrong?
Thanks!
Offer Baruch
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