Another noob question: How bad is a non-optimal raidz configuration?

[Diogenes Platterwort]

I was planning to do raidz2 with my 5 drives, but freenas is complaining that this is non-optimal for performance, but I can't find anything that says how big a performance hit this will cause.

I don't need great performance anyway, but I don't want to cripple myself unnecessarily. So how big a difference are we talking about, and is it primarily write performance that's affected?

 

[survive]

Hi Diogenes,

When I moved from raidz1 to riadz2 it cost me about 40MB/s on the "write out a big file using dd" test. I went form around 480MB/s to 440 MB/s.....totally worth it.

Here's what I would do....try it and see. FreeNAS has a couple of benchmark utilities included (iozone, xdd), you could always try the "dd" drag race, and set up a share and see if it performs well for you....that's really the acid test. If you have space for a 6th drive now would be the time to score another drive which would put you at a 6 drive riadz2 which is a magic number for drive count you might find that it's just as fast as a 5 drive raidz1 with the extra resiliency you really want.

-Will

 

[Diogenes Platterwort]

Thanks for the response. Unfortunately I can't fit another drive in this box, but a 10-20% speed decrease would be fine. I'm running some tests now.

 

[Diogenes Platterwort]

Just to follow up, performance is slow with the non-optimal array, but I tried a more optimal arrangement and it was still slow, so I don't think the performance difference due to the raidz2 config is significant enough to matter for my slow machine.

 

[cyberjock]

So what hardware are you using? Sounds to me like you are probably using less than the minimum requirements..

 

[Diogenes Platterwort]

It's an old Precision 670 workstation, with two 3.0ghz single-core xeon processors and 4 gigs of RAM. As I mentioned in my other question, I'm able to upgrade the RAM, but there's not much point in doing so with the 32 bit version.

 

[gpsguy]

insufficient RAM and cache being disabled are probably affecting your performance numbers.

If you can't add RAM, consider switching to UFS instead of ZFS.


Sent from my phone

 

[Diogenes Platterwort]

I'm not really that worried about the performance. Slow is fine, as long as it's stable. My big concern wasn't so much fast performance as instability or unreliability. I guess I didn't really ask the right question originally.