[XCSSA] NAS the VIA EPIA way

[X-otic Computer Systems of San Antonio]

On Jul 1, 2009, at 12:40 AM, X-otic Computer Systems of San Antonio  
wrote:

>> We have seen random I/O still be a significant issue on a
>> RAID5 versus a RAID10.
>
> Yeah.. I'm more talking about just regular OS I/O. But you're right  
> too if the
> server is being used as a streaming media (video) box.. the RAM  
> would fill up
> (or empty out) very quickly waiting on I/O to/from RAID-5.

True, but in the case of streaming video, you're dealing with less  
random I/O. I could see a RAID5 keeping pace with a GigE connection  
here. I would imagine space efficiency might be more important here so  
it might be worth the trade-off. RAID10 only offers 1/2 the capacity  
of the total number of drives which can make it less than ideal for  
some situations (such as a home NAS/media server). I would be curious  
how the stripe size offsets some of this too. If videos are being  
stored, the stripe size can likely be a lot bigger.

And, with XFS, a RAID5 might actually have acceptable performance  
(don't forget to turn off write barriers). Again, we've only had  
exposure to a RAID5 with ext3, which is like my least favorite file- 
system on Linux :)

>
>> but you will
>> likely never see a RAID5 performance like a RAID0 for random I/O.
>> Sequential I/O, however, isn't near as bad on a RAID5.
>
> Speaking of RAID I/O speed.. I've always wondered.. do you see much/ 
> any I/O
> speed degradation on RAID-10 over say pure RAID-0?  Or is it more a
> spindle-count issue?

For reads, you should see it outpace both a RAID1 and RAID0. For  
writes, the RAID0 might win out over a RAID10, but my guess is not by  
all the much. Truth be told, however, we've never run a test that  
compared a 4-drive RAID0 or RAID1 to a 4-drive RAID10. Even if we did,  
the slight performance differences you might see in a RAID10 are not  
big enough to warrant using a RAID1 or RAID0 in my opinion. Well, if  
it's scratch space, a RAID0 would be a maybe; but having a 4-drive  
RAID1 array would just be silly :)

>
>
>> Among other things, with XFS you can
>> describe the underlying drive configuration and make sure it  
>> optimizes
>> for it. So, in theory, a RAID5 might not be all that bad. But it sure
>> does suck for ext3 with MySQL :/
>
> Yeah.. What happened to the XFS support?  I heard that it was being  
> tested..
> and "possibly"targeted for RHEL 5 U3..?

I talked to BJ about this and he said Red-Hat offers support for XFS  
for some stupid per year fee. It's basically just a kernel module.  
Jerks. From what I understand, XFS was supposed to be in 5.3 as a beta  
type of thing. I haven't seen it yet, but then again I haven't been  
looking hard.

It's not difficult to add though. In fact, Red-Hat already ships with  
some XFS tools. Everything but the $%^@ing kernel module! So you can  
easily add that in and then call it done. We were passing that idea  
around on the DBA team to see if BJ and the RPM guys would be down.  
Way too soon to say though. Even if we did, it would be a pretty big  
one-off, at least initially. And it complicates kernel upgrades.

>> LSI MegaRAID SATA 150-6. It's from 2004 I think. I believe it has  
>> 64MB
>> of onboard cache (non-upgradable).
>
> Hmm.. a little small.. 2004?  Not SATA-II then?
> Ahh yeah... It's PCI-64 but only 150MB/sec (not 300).
> A littel slow to put new 1TB SATA-II drives in.

150MB per link though, so your aggregate is going to be limited by the  
PCI or PCI-X bus. The only time that hurts would be on a read. Writes  
should not be cached on the hard-drive's buffer since there is already  
the battery backed up cache on the RAID controller. That means by the  
time the RAID controller does a write, it will be limited to the spin  
speed, etc. It's not AS fast though, I'll admit, and I don't think  
native-command queueing works on SATA-1 (even if the drive supports it  
via SATA-II) though I could be wrong.

But if you want to buy an LSI controller new, be prepared to spend up  
into the hundreds. I haven't decided on the price for it or the  
drives, but I don't have any use for it so I wasn't planning on trying  
to sell it for anything crazy. If no one wants it, I will probably put  
it in the Goodwill pile if I can't find a Racker or someone local to  
grab it up. I'm sure I could sell it on eBay but that's too much of a  
pain in the ass :)

> Good chat.. looking forward to your presentation man.. send me some
> bullets/links/whatever as soon as you're able.

Let me get passed my RHCE, and catch up on some of my other hobbies  
and I'll let you know :) Looks like I have a little while yet so I  
should be able to do something. Of course, if I finish the synth, I'm  
going to bring that instead :)

Tim