June 07, 2007
Comments
The numbers are no surprise since you are doing half the writes as RAID 1. Are you afraid of losing all your data if one of the drives go bad? If you are planning to rely on SMART to tell you when to replace your drive, you could be in for a bad surprise as SMART only tracks a small amount of factors that could lead to drive failure. Of course, when Leopard comes out, you can switch to ZFS. Posted by: Steve Jenson on June 7, 2007 11:35 AMYou are only testing sequential I/O. Something like Bonnie or iozone would give you a more complete picture. ZFS rocks. I have it running on my Sun ultra 40 M2 Solaris home server, with 6 750GB drives in a RAID-Z2 configuration, and benchmarked it at well over 160MBps sustained I/Os. The slow RAID 1 reads would suggest the OS X RAID implementation is not well tuned. It should be able to load-balance I/Os across both drives when reading. I'm not surprised at the low performance of the external RAID. Software RAID on a 2GHz+ Xeon is always going to be way faster than hardware RAID on whatever wimpy storage processor that's embedded in the enclosure, probably not much faster than a 200MHz ARM. In any case, the latency of going through multiple layers of translation from the system bus to slower intermediate buses to USB to SATA and back is also a big drag on performance. Posted by: Fazal Majid on June 7, 2007 01:33 PMSteve, thanks for pointing out the need for monitoring. I did setup the smartmontools (from http://smartmontools.sourceforge.net/). Fazal, the performance that your filesystem gets is really impressive! On the setup I mentioned, during the recovery from the backup I only got some 12MBps (720GB copied in about 15 hours from the external RAID drive). This rate was severely limited by the external USB drive, which is 7 times slower than the internal RAID 0 for reads. Once Leopard is out I will most likely upgrade my file systems to use ZFS. It looks like a winner! Post a comment
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