It's not clear what disks sold with the Enterprise™©® label really do to justify the big price difference. Often it seems like the hardware is exactly the same, but the firmware behaves differently, notably to report errors faster. In desktop environments, you want the disk to try hard to read bad sectors, but in RAID arrays it's better to give up quickly and let the RAID controller know, otherwise the disks might timeout from the controller's point of view, and the whole disk might be incorrectly considered dead and trigger a spurious rebuild.
So I recently benchmarked the Hitachi 7K3000 against two other "enterprise" disks, the Western Digital RE4 and the Seagate Constellation ES.
The line up
- Hitachi 7K3000 model: HDS723020BLA642 – the baseline
- Western Digital (WD) RE4 model: WD2003FYYS
- Seagate Constellation ES model: ST2000NM0011
Both enterprise disks cost about $190, so about 90% more (almost double the price) than the Hitachi. Are they worth the extra money?
The testI ended up using SysBench to compare the drives. I had all 3 drives connected to the motherboard of the same machine, a dual L5630 with 96GB of RAM, running Linux 2.6.32. Drives and OS were using their default config, except the "deadline" IO scheduler was in effect (whereas vanilla Linux uses CFQ by default since 2.6.18). SysBench used
O_DIRECTfor all its accesses. Each disk was formatted with ext4 – no partition table, the whole disk was used directly. Default formatting and mount options were used. SysBench was told to use 64 files, for a total of 100GB of data. Every single test was repeated 4 times and then averages were plotted. Running all the tests takes over 20h.
ResultsA picture is worth a thousand words, so take a look at the graphs. Overall the WD RE4 is a clear winner for me, as it outperforms its 2 buddies on all tests involving random accesses. The Seagate doesn't seem worth the money. Although it's the best at sequential reads, the Hitachi is pretty much on par with it while being almost twice cheaper.
So I'll buy the Hitachi 7K3000 for everything, and pay the extra premium for the WD RE4 for MySQL servers, because MySQL isn't a cheap bastard and needs every drop of performance it can get out of the IO subsystem. No, I don't want to buy ridiculously expensive and power-hungry 15k RPM SAS drives, thank you.
The raw outputs of SysBench are available here: http://tsunanet.net/~tsuna/benchmarks/7K3000-RE4-ConstellationES