Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Fri, Apr 24, 2009 at 12:18:47PM +0200, Dominik Klein wrote: > > ah. and btw. do not use "none", > > that is to say, do NOT use "no-disk-drain". in general, that setting > > will violate write ordering constraints, and gives very little benefit. > > it is useful only in very special circumstances. > > Namely on known-to-work-well battery-backed-write-cache controllers. Is > that about right? nope. on known-to-not-reorder-requests-and-no-volatile-caches-involved backends. which are exceptionally rare. in linux, you need to be on top of "elevator=noop", and no driver involved, or SAN iSCSI/FC target (or sata on-disk circuitry, for that matter) is allowed to even think about re-ordering. if (and _only_ if) nothing in the stack re-orders writes, (and won't lose writes on power loss or crash), then barriers become pretty much no-ops (with possibly performance hurting side-effects), and any waiting on already issued requests can be left out. -- : Lars Ellenberg : LINBIT | Your Way to High Availability : DRBD/HA support and consulting http://www.linbit.com DRBD® and LINBIT® are registered trademarks of LINBIT, Austria. __ please don't Cc me, but send to list -- I'm subscribed