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12 disk Linux raid6 - performance?

post #1 of 9
Thread Starter 
I want to build a 12 disk storage server. I will initially start with around 6 and expand as needed. I think I've pretty much decided that Linux md would be my preferred pooling method but my concerns is performance.

I've heard many claim that software raid 5 and 6 perform very poorly. How poor? My minimum requirement is 125MBps read and write but ideally I want to achieve ~250MBps read and write saturating 2xGb NICs.

I'm planning to go with an existing E6420 CPU. Would this be sufficient? Would going faster/more cores improve raid performance?

- Why not ZFS?
I have considered ZFS and raidZ but based on what I read raidZ cannot be expanded to span new disks unless I rebuild the array. Not good because I plan to expand this array gradually as needed. md with LVM I read is fairly easy to do this on. Please correct me if I'm wrong.

- Why not Unraid/flexraid/hardware controller?
I'm sticking to free and open. I don't want to deal with licensing and/or proprietary protocols for accessing my data.

Thanks for any help
post #2 of 9
You're performance will be fine - most people who state software RAID is poor are either clueless (stuck in the 80s), using Windows (Windows RAID is all over bad) or they have things set up incorrectly. Software RAID arrays can easily be made that are faster than hardware arrays - after all, a full blown quad core CPU at 3GHz+ with large quantities of fast internal cache & external RAM is a little faster than a tiny XOR CPU at 800MHz with no cache and only a little DDR2 for company. And the big advantage with software RAID is that when you bottleneck one controller or interface, you can simply add another and keep going faster.
post #3 of 9
Thread Starter 
Thanks. Sounds logical to me. Do you think a quad core would improve raid performance over dual?
post #4 of 9
for a 12 disk fileserver? No. Won't be any difference to a Sempron.
post #5 of 9
In terms of performance you could go raid6+0, 2 raid 6 Rrays and then 0 them
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post #6 of 9
Thread Starter 
Quote:
Originally Posted by the_beast;13925508 
for a 12 disk fileserver? No. Won't be any difference to a Sempron.

Thanks good to know.
Quote:
Originally Posted by 1337LutZ;13925537 
In terms of performance you could go raid6+0, 2 raid 6 Rrays and then 0 them

I want performance but more importantly I need lots of space tongue.gif


Edit: err for some reason I read that as raid6+mirroring.. 6+0..I might consider that. Thanks.
post #7 of 9
@OP

You're on the right track. md RAID + LVM really is the way to go. Be warned concerning your choice of filesystem: ext4 is the natural choice, but while you can create a single ext4 filesystem of 1EiB, the tools will only go to 16TiB, so beyond that point fsck will fail.

Personally I would suggest JFS as a filesystem, it's a good, all-round performer.
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post #8 of 9
Thread Starter 
Thanks. I'll proceed on with md and LVM when I get my parts.

I didn't know about the ext4 tool limitation. Good to know.

I too like JFS. I run JFS on my current storage and I probably would have gone JFS again anyway. I like getting a second opinion though.
post #9 of 9
I have an 8x2TB Samsung green drive MDADM RAID 6. I recently upgraded it from an AMD 4800+ (2.5ghz) dual core with 4gb DDR2 800mhz ram. With that hardware i got ~180MB writes and ~260-280MB/s reads.

Just upgraded to a Q6600 (overclock 2.4ghz->2.88ghz) and 8gb DDR2 ram. reads are now around ~398MB/s and writes are at 411MB/s (writes faster than reads on a raid 6 :S)

So there are some rough performance factors for you with mdadm and raid 6
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