From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: about raid5 recovery when created Date: Wed, 30 Dec 2009 13:55:02 +1100 Message-ID: <20091230135502.6a21441f@notabene.brown> References: <20091210145931.46ccbfe4@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: mjevans1983@gmail.com Cc: linux-raid List-Id: linux-raid.ids Thanks. I have applied this patch. NeilBrown On Wed, 9 Dec 2009 21:52:18 -0800 (PST) mjevans1983@gmail.com wrote: > On Wed, Dec 9, 2009 at 7:59 PM, Neil Brown wrote: > > 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 imme= diately - 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 p= ass > >> if I knew I could vastly speed up post-assembly performance. =C2=A0= 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 b= e happy to > > accept it. > > > > NeilBrown > > >=20 > diff --git a/mdadm.8 b/mdadm.8 > index f8f240a..29e098b 100644 > --- a/mdadm.8 > +++ b/mdadm.8 > @@ -648,6 +648,12 @@ data will be affected unless you actually write = to the array. It can > also be used when creating a RAID1 or RAID10 if you want to avoid th= e > initial resync, however this practice \(em while normally safe \(em = is not > recommended. Use this only if you really know what you are doing. > +.IP > +When the devices that will be part of a new array were filled > +with zeros before creation the operator knows the array is > +actually clean. If that is the case, such as after running > +badblocks, this argument can be used to tell mdadm the > +facts the operator knows. >=20 > .TP > .BR \-\-backup\-file=3D -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html