Dave Chinner put forth on 8/7/2010 5:13 AM: > On Thu, Aug 05, 2010 at 03:33:17AM -0500, Stan Hoeppner wrote: >> Neil Brown put forth on 8/4/2010 5:24 PM: >> >>> Both page-cache and read-ahead work at the filesystem level >> >> Are you referring to /sys/block/sdx/queue/read_ahead_kb? I'm pretty sure this >> works below the FS level and below the partition level. This read_ahead works >> at the block device level. At least for individual or JBOD. > > That number is used to initialise the default readahead value for > any file descriptor opened on the filesystem. readahead is tracked > per-fd at the page cache level, so is effectively at the filesystem > level, not the block device. > >> Are you saying this setting gets ignored by the kernel if/when mdadm, LVM, >> and/or crypto are used? > > Only the value from the block device the filesystem sits on is used. > i.e. if you are using /dev/md0, then the filesystem uses the value > from /sys/block/md0/queue/read_ahead_kb and ignores all the ones set > on the /dev/sdX devices that make up /dev/md0. Thanks for the clarification/education Dave. -- Stan _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
