PE4600 RAID question

Alexander Lazarevich alazarev at hera.itg.uiuc.edu
Thu Dec 12 15:41:00 CST 2002


We have a PE4600, Dual 2.8GHz, 4GB RAM, PERC3/QC RAID controller (2
internal channels and 2 external channels), with 8 X 73GB drives in the
non-peripheral bay (I don't know what its called, but its the 4x4 drive
bay built into the machine), and we also have 2 X 73GB drives in the
peripheral bay.

When we got the machine from DELL, we asked for the 2 drives in the
peripheral bay to be attached to the first internal channel on the PERC3
in a RAID 1 configuration, and the 8 drives in the non-peripheral bay to
be attached to the second channel on the PERC3 in a RAID 5 configuration.
They sent it to us exactly as we asked. No problem there.

However, once we installed RH linux 7.3 to it and started running some
filesystem read/write test, we noticed that the best we could get on the
RAID 5 array was about 46MB/sec sequential writes. We are not too happy
about this.

So, in an effort to improve the RAID 5 performance, I esentially want
to try spliting the 8 drives accross two channels (4x4), to hopfully
increase my sequential write performance. What I want to try and do is
this:

Remove the 2 X 73GB drives (RAID 1 array) off of the 1st channel of
the PERC3 controller, and put those drives onto the PERC4 controller that
is built into the motherboard (I think its a PERC4 that's built into the
motherboard, and the manual shows me how to activate it, that's no problem
there).

Then, I'd like to reconfigure the PERC3 internal channels so that 4 of the
drives in the non-peripheral bay are on the 1st of the internal channels
on the PERC3, and the other 4 drives are on the 2nd internal channel of
the the PERC3. Then I want to reconfigure the RAID so that all 8 drives
are in the same RAID 5 array.

My theory is that if the RAID 5 is split accross two channels, the
performance will be better.

However, The manual shows absolutely nothing about how to reconfigure the
cabling to the drives in the non-peripheral bay. That non-peripheral bay
is locked down, and I'm not even sure I'm able to split those drives
accross channels.

My question is: can those drives in the non-peripheral bay be split
accross two channels?

Also, does anyone have any idea if this will increase filesystem write
poerformance?

Thanks in advance!

Alex
---                                                        ---
   Alex Lazarevich | Systems | Imaging Technology Group
   alazarev at itg.uiuc.edu | (217)244-1565 | www.itg.uiuc.edu
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