On Thursday, January 28, 2010 10:48 PM, Ross Walker wrote: > > On Jan 27, 2010, at 7:50 PM, Christopher Chan<christopher.chan at bradbury.edu.hk > > wrote: > >> >>> Sorry to be the bearer of bad news, but on top of LVM on CentOS/RHEL >>> the best assurance your going to get is fsync(), meaning the data is >>> out of the kernel, but probably still on disk write cache. Make sure >>> you have a good UPS setup, so the disks can flush after main power >>> loss. >> >> Or turn off write caching... > > Have you tried doing any kind of write with write caching turned off? > It is so horribly slow to make it almost useless. If they needed the performance in the first place, I doubt they would be using md raid1. You want performance and reliability? Hardware raid + bbu cache. Otherwise, it is turn off write caching unless the i/o path supports barriers. > > If you need to turn write-caching off then I would start looking at > SSD drives with capacitor based caches. > How do those compare with bbu nvram cards for external data + metadata journaling?