From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: raid1 mirror optimizations Date: Wed, 26 Jan 2011 10:49:50 +0100 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 25/01/2011 19:56, Roberto Spadim wrote: > hi guys... i have a damaged disk... > i=B4m using raid1 > the computer crashed with the floor :P hihiih sorry, but the disks ar= e > damaged at the same position > check: http://www.spadim.com.br/hd%20agra.zip > the problem: since raid1 (mirror) is done with real mirror, the disk > position are the same... > if i was using a mirror but on disk 1 i write from beggining to end, > and disk 2 from end to beggining , i don=B4t crash the disk at the sa= me > position, for disk 1 i crash it some bytes, for disk 2 i crash some > others bytes, since beggining is a small cilinder and end a bigger, i > could loose less information than mirror > could we implement a 'inverted' mirror? just for hard disks (for ssd > it=B4s a small loss of cpu/memory) > thanks > If you are worried about the disks being in the same position, then I=20 assume you mean the heads were in the same position when they crashed=20 into the disk. If that's the case, then it doesn't really matter too=20 much if the same bytes on the disk were hit - your disks are trashed=20 anyway, and you'll need expensive professional recovery services to dea= l=20 with it. If you are not talking about head crashes, and merely about corruption=20 because the disks were being written to in the same place on both disks= ,=20 then the layout on the disk will make little difference - the same data= =20 will be written to the same logical place at roughly the same time. It= =20 doesn't matter where this data is located physically on the disk, since= =20 it is the data that matters. The same thing actually applies to head=20 crashes too. If you really want an "inverted" mirror, there is an easy way to get=20 much of the same effect. Instead of setting up raid1, use raid10 with=20 "far 2" positioning. The effect is roughly like this: disk1 (stripe 1) (mirror of stripe 2) disk2 (stripe 2) (mirror of stripe 1) So the two copies of the data are in different physical positions on=20 each disk. It's not a full reversal, but you can think of disk 2 as=20 being split in two and its two halves swapped. -- 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