Christian Nygaard wrote:
I'm considering how to design a new file server with a 3ware 9650se RAID
controller. How much
would you estimate the impact to be on sharing /home and the operating
system on one raid 6 set?
/home is mostly read only accesses with a ratio 10:1 read/write. I'm a
little bit concerned that the log writes
in /var/log could impact read performance on /home causing disk head
movements or that a little/non issue with
modern Raid controllers?
What would give best performance
Scenario 1
8*500G Raid 6 /home and operating system
Scenario 2
6*500GB Raid 6 /home
2*250GB Raid 1 operating system
Looking for feedback
Carving up a hardware device into partitions results in a performance
penalty that goes up to 30%. eg: A single /dev/sda will perform better
than if it were carved in /dev/sda1 /dev/sda2.
I am not sure how a single /dev/sda used as a physical volume which is
then carved logically performs however. So my suggestion would be
6*500GB Raid6 /home and 2*250GB raid 1 operating system (remember, if
the mirror is carved up, you will receive a performance penalty).
The performance penalty is incurred regardless of what I/O patterns a
particular partition has so your concern about log writes to /var/log
affecting /home are correct but not just due to the writes...the writes
merely affect the degree of the performance penalty.
This was verified with SCSI disks, ATA disks and 3ware arrays but it was
a while ago. Perhaps things have changed in the latest kernels but with
Centos 4.4 at 2.6.9 I don't think Centos 4 kernels have those changes if
they exist.
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