Wednesday, August 4, 2010

Isilon Scale Out NAS

Isilon Scale Out NAS

Last week I sat through a presentation about Isilon's Scale Out NAS Platform. The technology and innovation behind Isilon is interesting and the features and benefits of scale out NAS are quite impressive. Having worked with the EMC Celerra, and Microsoft Windows based NAS devices, I was accustomed to the usual NAS setup: 2 or more NAS heads in an N+1 high availability cluster, with the NAS heads connecting to back-end storage and converting block based data to file based data. Scale out NAS, as implemented by Isilon gets rid of the individual NAS heads and combines the entire unit into one big cluster.

Features of scale out NAS I am most impressed with are:

1) No individual NAS heads. The scale out NAS device is made of individual hardware nodes. These nodes are clustered together and work seamlessly with each other. There is no longer one dedicated standby node, each node is capable of taking over if another node fails.

2) All resources are pooled together. There are no RAID groups, or back-end LUNS. A file system spans over the entire storage system. This leads to high IOPS, redundancy and reliability. However, I don't know how Isilon balances the filesystems on the back-end. As you keep on creating file systems, wouldn't the last filesystem perform poorly compared to the first filesystem?

3) There is no RAID in the traditional sense. Unlike other NAS devices where you define what RAID protection you want for your particular file system, in the Isilon scale out NAS device you define how much redundancy you want for your data. You can configure N+2 data protection and that will protect your data against 2 disk failures or two node failures. All data is striped across all nodes in the cluster, so no one disk or node contains all your data. The best feature? You can define protection per file, per directory, or cluster. Compared to other NAS devices where you define protection at the file system level, in the Isilon systems you have complete flexibility in choosing your protection scheme.

4) Hardware nodes can be added while the NAS cluster is in production and the NAS balances the data across the new nodes. Maybe this answers my concern about file system performance in number 2.

5) No more long rebuild times after disk failures. Since there is no RAID, there are no parity drives. When a disk fails, the free space on all the remaining drives is used to recreate the data. Although what happens when the system is nearly full, does rebuild performance deteriorate as free space gets low?

One thing I will have to experience myself is the promise of linear performance. In traditional NAS, performance increases rapidly as disks are added, but after a certain point performance becomes nearly flat. Each new disk shows diminishing returns in performance. Isilon promises linear performance gains, that is as more disks are added, performance increases by that much. I am not doubting this, but this is something I will have to test myself and verify.

In conclusion, I was very impressed with the Isilon scale out NAS. Now if I only had the money :)