From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Stripe dirty bitmap Date: Sun, 04 Jul 2010 21:24:50 -0400 Message-ID: <4C313462.8090403@tmr.com> References: <4C3126C0.4050709@tmr.com> <20100705110203.01502ac1@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100705110203.01502ac1@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Linux RAID List-Id: linux-raid.ids Neil Brown wrote: > On Sun, 04 Jul 2010 20:26:40 -0400 > Bill Davidsen wrote: > > >> Sure would be nice to have md track whole never written stripes, so >> creating an array didn't have to be done over a three day weekend. When >> any part of a virgin stripe was written it could then be initialized >> properly, and when a virgin stripe was read zeros could be returned >> without disk i/o. It doesn't matter that the reads are done in parallel, >> with modern disk the bus is the bottleneck. With eSATA arrays the bus is >> slow to start with, passing TB through it should be avoided if possible. >> >> > > Sure would. > Have to have a copy on each drive, I think? Use a bit for a group of N stripes or one per stripe? Put N in the metadata? I'd use stripe_cache_size, but that changes. As disk gets cheap (1.5TB for $65 this weekend?) bus speed is being an issue, more so with software raid which does the io out of system memory. -- Bill Davidsen "We can't solve today's problems by using the same thinking we used in creating them." - Einstein