[SATLUG] Filesystem/RAID advice

Brad Knowles brad at shub-internet.org
Tue Oct 12 19:09:43 CDT 2010

On Oct 12, 2010, at 5:51 PM, travis+ml-satlug at subspacefield.org wrote:

> Most of us avoid it by using a network file system, but performance
> does suffer.

For the same type of application, NFS can be a lot faster than a poorly implemented local RAID.  I have a Data Robotics DROBO, and I've benchmarked the thing (with fast drives) and compared those benchmarks against a similar configuration on an Infrant ReadyNAS NV+.  The ReadyNAS was much faster than the DROBO, in part because the ReadyNAS used Gigabit Ethernet whereas the DROBO used only USB or FireWire, and the slow CPU in the DROBO meant that it couldn't keep up with either USB or FireWire, and the ReadyNAS won hands-down.

Compare the ReadyNAS against a more modern (and much faster) DROBO model, and then it comes down to the filesystem.  If I could get a ReadyNAS-like device that was running OpenSolaris or FreeBSD and ZFS, I'd be willing to bet that I could build an NFS-on-ZFS configuration that would smoke both the ReadyNAS and the DROBO.  But then there aren't any commercial ReadyNAS or DROBO-like appliances that are built on OpenSolaris or FreeBSD with ZFS, at least not that are affordable for the SOHO market, so it would be more complex to install, configure, and administer.

> Regarding RAID, yeah, RAID 0 (no mirroring) or 10 (mirroring) is
> best for performance.  Everything else tends to tank it, due to
> something I recall being called write amplification.  Google did
> a study and picked 10 over 5 due to the fact that it required
> fewer I/O operations at the expense of capacity, which is in
> more plentiful supply.

Again, it depends on the specific implementation.  With simple RAID implementations, you are correct.  However, more complex RAID implementations (including some of the good hardware RAID controllers) can get create instances where RAID-5 volumes are no slower than RAID-0 or RAID-10, at least with regards to throughput and perhaps I/O operations per second (IOPS), although RAID-0 or RAID-10 will pretty much always win on issues of latency.

Of course, these more complex RAID implementations are also a lot more expensive.

Brad Knowles <brad at shub-internet.org>
LinkedIn Profile: <http://tinyurl.com/y8kpxu>

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