Re: Performance degradation when using partitions

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Daniel Nilsson wrote:

On Tue, Nov 22, 2005 at 10:48:41AM -0500, Bill Davidsen wrote:
Daniel Nilsson wrote:
While setting up a software RAID-5 array I started looking into the
performance aspect of using partioned drives versus the whole disks
for a RAID-5 array. I have an Adaptec 2400a controller which through
the I2O kernel driver gives me access to 4x 250GB disks (JBOD mode).
Did you get an answer on this? And does it happen if you use the drives directly, /dev/hdN or /dev/sdN instead of using I2O? I didn't see an obvious speed penalty in raw access of drives vs. partitions, but I lacked the hardware to really match your setup, particularly the I2O use vs. direct access to /dev/sd[ef].

Bill,

No, I didn't get an answer on this. I've done some more experiments
with the drives, but since they are connected to an Adaptec 2400A RAID
controller (in JBOD mode) I need to go through some I2O driver in or
to see the drives at all. So I never have direct access to these
drives as /dev/hdN or /dev/sdN. There are however two different
drivers available for this RAID controller, one is the standard I2O
driver and the other one is the Adaptec dpt_i2o driver.

The results are the same though whether I use the Linux I2O driver or
the Adaptec dpt_i2o, the software raid array is rebuilding at roughly
half the speed when the drives are partioned. I don't know what other
data to provide in ordet to get any further in the testing.

Unfortunately, until someone else has the time and interest to make more tests I don't see a good next step. I might be able to at least do some better quantified tests later this weekend, but I have no I2O devices, so it isn't going to tell much.

--
bill davidsen <[email protected]>
 CTO TMR Associates, Inc
 Doing interesting things with small computers since 1979

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