ReadyNAS Pro iSCSI benchmarks on Mac OS X

I've been using ReadyNAS products since they were still being sold by Infrant, but it wasn't until the latest iteration that they became incredible performers. The Netgear [ReadyNAS Pro]( has 6 SATA drive bays and funcations as just about every kind of server one could want (for a home office, that is). My first ReadyNAS Pro has 7.89 TB accessible (1 disk redundancy), and is being used as a backup volume for 4 separate machines. SuperDuper! clones volumes to disk images hosted on the NAS, and it also serves as a Crashplan repository (through a Mac Mini running Mac OS X Server). The NAS also hosts all of my media (e.g. videos, music, installer disk images), serving media through shared volumes and various media servers (like UPnP to a Playstation 3).

I [decided in July](/journal/2010/07/05/using-iscsi-with-readynas-pro-and-mac-pro/) that I wanted to move my still images off of my Mac Pro onto network storage, but [early tests using iSCSI](/journal/2010/08/11/netgear-readynas-pro-iscsi-performance-benchmarks/) showed inconsistent performance. Using a heavily-accessed ReadyNAS Pro to host an iSCSI volume seemed to be too much for the poor box.

After some deliberation, I decided to purchase a second ReadyNAS Pro to host a dedicated iSCSI volume for my Mac Pro. When it arrived, I put 5 x 2TB drives (old Seagate Barracuda LPs) and 1 x 1TB drive into it and did a factory reset. It initially allocated 927 GB per drive, but did a volume expansion afterwards. After more than 24 hours, it came online with 8.81 TB accessible (2 drive redundancy). I immediately ran benchmarks on it.

**Network configuration:** my Mac Pro is connected to the ReadyNAS Pro via a gigabit ethernet cable (through its second gigE port) bypassing switches and routers. I manually assigned ip addresses and turned jumbo frame support on (MTU 9000). All traffic between the Mac Pro and ReadyNAS Pro is isolated from other LAN traffic and internet traffic. I'm using [ATTO Xtend SAN iSCSI initiator]( because the free GlobalSAN doesn't work in 64-bit mode.

As a dedicated iSCSI box, the ReadyNAS Pro is fantastic for reads of all kinds. It has fantastic random access transfer speeds, and the transfer curve goes up from just over 13 MBytes/sec at 4KB to between 100-115 MBytes/sec at write sizes over 256 KB.

Writes show somewhat less consistent performance, although the tests that QuickBench run always dip down when 128KB writes are attempted. Once write sizes reach over 2MB, transfer speeds stabilize at between 80-90 MBytes/sec.

For reference, a 2TB Western Digital Caviar Green benchmarks at around 100 MB/s.

I thought it would also be interesting to compare maximum throughput with other drives and RAID setups I've tested in the past:

iSCSI can't really keep up with my current disk subsystem, which consists of 4 striped 2TB Western Digital Caviar Black drives, but it is pretty impressive nonetheless, since the box lives in my closet (it's silent, from my workspace) and can handle two drive failures (out of its six drives) without losing any data.

I also compared small block transfers:

For 4KB random reads, the iSCSI box is faster than everything except one of the SSDs. Of course, this does not take latency into account, which (I'm sure) makes a huge difference.

Practically, I only access most of the files stored on the iSCSI volume when Adobe Lightroom pulls down a RAW file. So far, there has been no noticeable difference in Lightroom performance when working with images stored on my local drive and images stored on the iSCSI volume. I will need more time to verify this claim, but everything is looking good so far!