Hello again, FYI the Bugzilla bug of the problem. https://bugzilla.redhat.com/show_bug.cgi?id=520655
Thanks for now, Offer Baruch _____________________________________________ From: עופר ברוך [mailto:[email protected]] Sent: Tuesday, August 04, 2009 1:47 PM To: '[email protected]' Subject: z/Linux dasd performance issue 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 ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
