Yeechang Lee wrote:
[Also posted to comp.sys.ibm.pc.hardware.storage,comp.arch.storage,alt.comp.hardware.pc-homebuilt,comp.os.linux.hardware.]
I'm shortly going to be setting up a Linux software RAID 5 array using
16 500GB SATA drives with one HighPoint RocketRAID 2240 PCI-X
controller (i.e., the controller will be used for its 16 SATA ports,
not its "hardware" fakeraid). The array will be used to store and
serve locally and via gigabit Ethernet large, mostly high-definition
video recordings (up to six or eight files being written to and/or
read from simultaneously, as I envision it). The smallest files will
be 175MB-700MB, the largest will be 25GB+, and most files will be from
4GB to 12GB with a median of about 7.5GB. I plan on using JFS as the
filesystem, without LVM.
A few performance-related questions:
* What chunk size should I use? In previous RAID 5 arrays I've built
for similar purposes I've used 512K. For the setup I'm describing,
should I go bigger? Smaller?
I am doing some tests on this right now (this weekend), because I don't
have an answer. If I get data I trust I'll share it. See the previous
thread on poor RAID-5 performance, use a BIG stripe buffer and/or wait
for a better answer on chunk size.
* Should I stick with the default of 0.4% of the array as given over
to the JFS journal? If I can safely go smaller without a
rebuilding-performance penalty, I'd like to. Conversely, if a larger
journal is recommended, I can do that.
I do know something about that, having run AIX for a long time. If you
have a high rate of metadata events, like create or delete file, large
journal is a must, and I had one on another array with small stripe size
to spread the head motion, otherwise the log drive became a bottleneck.
If you are going to write a lot of data to this array, mount it
"noatime" to avoid beating the journal and slowing your access.
Be sure you tune your readahead on each drive after looking at the
actual load data. Think "more is better" but "too much is worse," on that.
* I'm wondering whether I should have ordered two RocketRAID 2220
(each with eight SATA ports) instead of the 2240. Would two cards,
each in a PCI-X slot, perform better? I'll be using the Supermicro
X7DVL-E
(<URL:http://www.supermicro.com/products/motherboard/Xeon1333/5000V/X7DVL-E.cfm>)
as the motherboard.
My guess is that unless your m/b has dual PCI bus (it might), and you
have 2 and 4 way memory interleave (my supermicro boards did the last
time I used one), you are going to be able to swamp the bus and/or
memory with a single controller.
Now, in terms of "perform better," I'm not sure you would be able to
measure it, and unless you have some $tate of the art network, you will
run out of bandwidth to the outside world long before you run out of
disk performance.
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979
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