From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Ciprian Dorin, Craciun" Subject: Re: Linux MD RAID 1 read performance tunning Date: Tue, 22 Dec 2009 19:08:25 +0200 Message-ID: <8e04b5820912220908s233c3bf9yf0fa9ba8deda693b@mail.gmail.com> References: <8e04b5820912220834m595f1aa6sf0071f99b4a5a144@mail.gmail.com> <20091222165225.GA2684@rap.rap.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20091222165225.GA2684@rap.rap.dk> Sender: linux-raid-owner@vger.kernel.org To: =?UTF-8?Q?Keld_J=C3=B8rn_Simonsen?= Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids 2009/12/22 Keld J=C3=B8rn Simonsen : > On Tue, Dec 22, 2009 at 06:34:55PM +0200, Ciprian Dorin, Craciun wrot= e: >> =C2=A0 =C2=A0 Hello all! >> >> =C2=A0 =C2=A0 I've created a 64G RAID 1 matrix from 3 real disks. (I= intend to >> use this as a target for backups.) >> =C2=A0 =C2=A0 Now while playing around with this array, I've observe= d that the >> read performance is quite low because it always reads from the disk = in >> the first slot (which happens to be the slowest...) >> >> =C2=A0 =C2=A0 So my questions are: >> =C2=A0 =C2=A0 * is there any way to tell the MD driver to load-balan= ce the reads >> between the three disks? > > It does not make sense to do distributed reading in raid1 for sequent= ial > files. This is because it will not be faster to read from more drives= , > as this will only make the reading from one drive skipping blocks on > that drive. In other words, in the time you use for skipping blocks o= n > one drive, you could just as well have read the blocks. So then bette= r > just read all the blocks off one drive, and then do other possible IO > from other drives. Aha. It makes sens now. But, does it mean that if I have parallel IO's (from different read operations) they are going to be distributed between the disks? > RAID10 is a modern form of raid1, which can do better distributed > reading, especially raid10,f2 is good for disks, while raid10,o2 may = be > better for SSDs. > > Best regards > Keld Unfortunately my setup forces me to use RAID1. (Because any of the three drives should be usable for a full recovery of the backup data.) (P.S.: Just to be clear, I'm not using RAID as a backup solution, but rather a redundancy solution for the backup solution. :) ) Thanks. -- 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