On Fri, Feb 26, 2010 at 11:11:07AM -0800, Mike Fedyk wrote: > On Fri, Feb 26, 2010 at 10:11 AM, Bill Pemberton > <wf...@viridian.itc.virginia.edu> wrote: > >> > >> Does the array have any kind of writeback cache? > >> > > > > Yes, the array has a writeback cache. > > > >> > >> Are all of the filesystems spread across all of the drives? Or do some > >> filesystems use some drives only? > >> > > > > In all cases the array is presenting 1 physical volume to the host > > system (which is RAID 6 on the array itself). That physical volume is > > made into a volume group and the filesystems are on logical volumes in > > that volume group. > > > > I wonder if the barrier messages are making it to this write back > cache. Do you see any messages about barriers in your kernel logs?
Most drives with writeback caches will honor the barriers. Most arrays with writeback caches will ignore them. Usually they also have their own battery backup, which should be safe enough to continue using the writeback cache. But, that depends on the array. Bill, I've got a great little application that you can use to test the safety of the array against power failures. You'll have to pull the plug on the poor machine about 10 times to be sure, just let me know if you're interested. If the raid array works, the power failure test won't hurt any of the existing filesystems. If not, it's possible they will all get corrupted, so I wouldn't blame you for not wanting to run it. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
