On Wed, Mar 27, 2013 at 7:25 PM, Kent Overstreet <koverstreet@xxxxxxxxxx> wrote: >> I've been using bcache since last summer, caching a 4x3TB raid5. >> >> Last week one of my disks died so after replacing it, I also got a new >> SSD and began to do some tests. There is something which, while not >> proving anything, worries me anyway. Better than describing it, just >> see this (caches were flushed before each hdparm): > > I think I may have finally figured this one out - bcache wasn't setting > readahead_pages, and raid5/6 needs it to be set based on the number of > devices in the array. Can you try the version I just pushed? Well, it improves it a little bit but there is still a wide gap, 1/3 worse than the raid directly: # hdparm -tT /dev/md0 /dev/md0: Timing cached reads: 23742 MB in 2.00 seconds = 11882.23 MB/sec Timing buffered disk reads: 1110 MB in 3.00 seconds = 369.83 MB/sec # hdparm -tT /dev/md0 /dev/md0: Timing cached reads: 24350 MB in 2.00 seconds = 12188.02 MB/sec Timing buffered disk reads: 1118 MB in 3.00 seconds = 372.39 MB/sec # hdparm -tT /dev/bcache0 /dev/bcache0: Timing cached reads: 23404 MB in 2.00 seconds = 11713.20 MB/sec Timing buffered disk reads: 724 MB in 3.00 seconds = 240.98 MB/sec # hdparm -tT /dev/bcache0 /dev/bcache0: Timing cached reads: 22638 MB in 2.00 seconds = 11330.39 MB/sec Timing buffered disk reads: 694 MB in 3.02 seconds = 230.08 MB/sec # hdparm -tT /dev/bcache0 /dev/bcache0: Timing cached reads: 23916 MB in 2.00 seconds = 11969.22 MB/sec Timing buffered disk reads: 686 MB in 3.00 seconds = 228.53 MB/sec -- Javier Marcet <jmarcet@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
