From mboxrd@z Thu Jan 1 00:00:00 1970 From: Goswin von Brederlow Subject: Re: Query regarding stripe management in linux md-raid Date: Fri, 01 May 2009 23:41:17 +0200 Message-ID: <87zldwjybm.fsf@frosties.localdomain> References: <18935.36392.65600.930716@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: (Kunal Kushwaha's message of "Wed, 29 Apr 2009 15:27:28 +0800") Sender: linux-raid-owner@vger.kernel.org To: Kunal Kushwaha Cc: Neil Brown , linux-raid@vger.kernel.org List-Id: linux-raid.ids Kunal Kushwaha writes: > Hi Neil, > > Thanks for your reply. I am trying to find out problems that I could > face later on. > > On Wed, Apr 29, 2009 at 7:15 AM, Neil Brown wrote: >> On Tuesday April 28, kunal.kushwaha@gmail.com wrote: >>> Hi, >>> >>> I am trying to put Linux raid in Box with 256 MB of RAM. The kernel= is >>> compiled with non-swappable memory management option. I looked into >>> raid5.c and found, it allocates one page for each chunk. =A0I am us= ing 5 >>> disks for 64k chunk size. considering my kernel is within 30 MB. >> >> That isn't quite right. =A0 It is not 1 page per chunk. >> raid5 maintains a stripe cache. =A0Each entry in the cache has one p= age >> per device, and there are 256 entries by default. >> So for a 5-disk array, that is 5*256 =3D=3D 1280 pages or 5MB (plus >> overhead). >> > > Sorry I missed to mention about stripe cache. Yes we will be using > only 5MB if we > consider page size is of 4k. > > I have one more doubt regarding this. How a page of 4k will be able t= o > store data of > 64k( my chunk size if of 64k) ? A chunk size of 64k does in no way mean all transactions are done in 64k chunks. What effect does chunk size actually do have? Was it just the amount of sequential data before the parity is rotated in a raid5/6. MfG Goswin -- 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