From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: about raid5 recovery when created Date: Thu, 10 Dec 2009 14:59:31 +1100 Message-ID: <20091210145931.46ccbfe4@notabene.brown> References: <389deec70912080501u6c6bc90ei2d34ef245a1dae9e@mail.gmail.com> <20091208131446.GA21130@cthulhu.home.robinhill.me.uk> <389deec70912080549h1b22489es612235ad29354d6b@mail.gmail.com> <20091208135600.GB21130@cthulhu.home.robinhill.me.uk> <389deec70912080603w47d7fda3jf021af169ac1c48c@mail.gmail.com> <4877c76c0912090030r266337afs394ecec463555258@mail.gmail.com> <389deec70912090329w65b7fa06hff8b75ad8f637307@mail.gmail.com> <20091210124359.4dd1a93a@notabene.brown> <4877c76c0912091934q8ce723ekb83f74bb06c401ba@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4877c76c0912091934q8ce723ekb83f74bb06c401ba@mail.gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Michael Evans Cc: hank peng , linux-raid List-Id: linux-raid.ids On Wed, 9 Dec 2009 19:34:04 -0800 Michael Evans wrote: > On Wed, Dec 9, 2009 at 5:43 PM, Neil Brown wrote: > > On Wed, 9 Dec 2009 19:29:04 +0800 > > hank peng wrote: > > > >> I think it is better to implement this function in kernel's md layer. > >> I wonder what Neil Brown think of this? > > > > I don't think it is worth the effort. > > You probably would save some CPU time as you don't need to XOR, but as has > > been said, we are usually IO bound, not CPU bound. > > > > With the current arrangement, you can start using the array immediately - you > > don't have to wait for the initial recovery to complete. > > If you zeroed all devices at create time, you would have to wait for that to > > complete before using the array. > > > > So I see very little gain, and significant cost. > > > > NeilBrown > > > > > > When I assemble an array I tend to have checked the devices before > hand; it would not be difficult to make the final pass a zeroing pass > if I knew I could vastly speed up post-assembly performance. As I > stated, it's merely a lack of clarity in the documentation. If you would like to create a patch against the man page, I would be happy to accept it. NeilBrown