Archive for February, 2011
I have run the entire gamut of virtual SAN appliances so far in my VMware lab environment, and I always come back to the Celerra UBER VSA. The best thing about this is that it’s free, and there’s no expiration. The LeftHand is easier to use, and has some neat clustering features, but it’s a 60 day license.
I don’t know about you, but there are times when I get busy, and don’t get a chance to touch the lab for weeks. 60 days is just not enough. I got the NetApp ONTAP 8.0 appliance as well, but it’s a pain to use unless you’re running VMware Server (who still runs that?) or Workstation.
Anyway, I’ve been struggling with the performance of the UBER VSA, and trying hard to find a way to make it faster. Thanks to Clinton Kitson, I was able to dramatically improve throughput and latency on my Celerra VSA. Time to deploy a VM from a template went from 30, down to 9 minutes.
Clinton says they may try to include this in the next UBER version, as long as there is consensus that it is beneficial and does no harm.
Here’s the tweak:
Login to the VSA using the root account. Password is nasadmin.
Type in this command: /sbin/swapoff -a
Then, go in and edit the sysctl.conf file using this command:
Add the following lines to the end of the file:
vm.dirty_background_ratio = 50
vm.dirty_ratio = 80
Ctrl+X to exit out. Save the file over the existing sysctl.conf.
Restart your VSA.
The screenshot below shows my VSA. I had already changed the caching settings, but here’s what happens by simply turning off the swap. You can clearly see the huge improvement in both latency and throughput.
Basically what we’re doing with these commands is telling the VSA not to swap. We’re also changing the way the underlying RedHat OS caches data before it writes to disk. Be aware that this does increase the risk of data loss, as we’re caching much more data in RAM before it’s written to disk. If data loss is a concern in your lab, you may want to stick with the standard settings. Also, my VSA has 6GB of RAM allocated. Still only a single data mover. Obviously more RAM = more performance when we’re turning up the caching.
Thanks to Clinton for pointing out these settings. It’s hard to find performance information on the EMC VSA. I hope this post helps you get more work done in your lab environment.