On Thu, Oct 21, 2010 at 12:06 AM, Peter Jeremy <peter.jer...@alcatel-lucent.com> wrote: > On 2010-Oct-21 01:28:46 +0800, David Dyer-Bennet <d...@dd-b.net> wrote: >>On Wed, October 20, 2010 04:24, Tuomas Leikola wrote: >> >>> I wished for a more aggressive write balancer but that may be too much >>> to ask for. >> >>I don't think it can be too much to ask for. Storage servers have long >>enough lives that adding disks to them is a routine operation; to the >>extent that that's a problem, that really needs to be fixed. > > It will (should) arrive as part of the mythical block pointer rewrite project. >
Actually BP rewrite would be needed for data rebalancing after the fact, as I was referring to write balancing that tries to mitigate the problem before is occurs. I was thinking of having a tunable like "writebalance=conservative|aggressive" where conservative would be the current mode and aggressive would be something like aiming that all devices reach 90% at exactly the same time, and avoid writing on devices over 90% altogether. The 90% limit is of course arbitrary, but seems like some kind of tripping point commonly. The downside of using aggressive balancing would of course be smaller write bandwidth, and the data written would not be striped so also subsequent read might have a drawback. Impact would depend heavily on usage pattern, obviously, but I expect most use cases would either not suffer from this, and it is arguable whether somewhat reduced bandwidth is preferable to serious write slowdown later down the road - the difference seems to be orders of magnitude, anyway. -- - Tuomas _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
