From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: Rotating RAID 1 Date: Tue, 23 Aug 2011 13:58:12 +1000 Message-ID: <20110823135812.62c56cee@notabene.brown> References: <4E497FB5.3030109@ivitera.com> <4E49849E.4030604@ivitera.com> <20110816084251.2d8e7831@notabene.brown> <20110816095517.757afc07@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: =?ISO-8859-1?B?Suly9G1l?= Poulin Cc: linux-raid List-Id: linux-raid.ids On Mon, 22 Aug 2011 23:45:53 -0400 J=E9r=F4me Poulin wrote: > On Mon, Aug 15, 2011 at 7:55 PM, NeilBrown wrote: > > Yes, add another one later would be difficult. =A0But if you know u= p-front that > > you will want three off-site devices it is easy. > > > > You could > > > > =A0mdadm -C /dev/md0 -l1 -n2 -b internal /dev/A missing > > =A0mdadm -C /dev/md1 -l1 -n2 -b internal /dev/md0 missing > > =A0mdadm -C /dev/md2 -l1 -n2 -b internal /dev/md1 missing > > =A0mdadm -C /dev/md3 -l1 -n2 -b internal /dev/md2 missing > > > > =A0mkfs /dev/md3 ; mount .. > > > > =A0So you now have 4 "missing" devices. >=20 > Alright, so I tried that on my project, being a low-end device is > resulted in about 30-40% performance lost with 8 MDs (planning in > advance), I tried disabling all bitmap to see if it helps and I get > minimal performance gain. Is there anything I should tune in this > case? More concrete details would help... So you have 8 MD RAID1s each with one missing device and the other devi= ce is the next RAID1 down in the stack, except that last RAID1 where the one = device is a real device. And in some unspecified test the RAID1 at the top of the stack gives 2/= 3 the performance of the plain device? This the same when all bitmaps are removed. Certainly seems strange. Can you give details of the test and numbers etc. NeilBrown -- 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