Which is faster /dev/mapper or /dev/cciss?

mohamed.a.mostafa · 03-30-2013, 01:29 PM

Dears,

First I'd like to inform you that I'm not an OS Related I'm an Oracle Applications Database administrator.

Thats why you may see my question is very simple

My Question is:
Which IO type is faster /dev/mapper or /dev/cciss?

I'm asking because while i upgrade an Oracle Applications over Linux Redhat 5 with two iterations (TEST and PROD) i found that the TEST was much more faster than the Production server where the # of processors in production is greater than the TEST Server.

By trubleshooting which task takes a long time, i found the date Insertion is the issue.

and I noticed that the df -h shows the database files resides on /dev/mapper/VolGroupx for PROD
and
/dev/cciss/c1d0p2 For TEST

So i guess this may be the root cause of that issue, Am i correct?

Is the Mapper Vol. Groups slower than the CCISS?
Also, may i ask you for a document may help me understand the different storage methodologies?

Many Thanks,
Mohamed

syg00 · 03-30-2013, 05:30 PM

One wouldn't think LVM should be intrinsicly (noticeably) slower than the base devices it is built on. No-one would use it if it was. However it does add another layer to the software stack as it is another block device driver.

Given this was an upgrade, it is likely this difference has always been in place. That would point to a possible configuration mismatch - which is much harder to diagnose - especially at the application layer.
Best place to start would be a read of the release guide for any highlights.

If it were me, I'd make sure the test environment reflected the Production it was supposed to be a test basis for ...

A quick search on "LVM on cciss" will pull plenty of relevant doco, but I doubt it will give what you seem to be asking. The hardware vendors don't release too much detail on how their kit works at the lower levels.