From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nagy Zoltan Subject: Re: component growing in raid5 Date: Mon, 24 Mar 2008 17:52:00 +0100 Message-ID: <47E7DC30.3040804@bteam.hu> References: <47E5FFB8.5030903@bteam.hu> <47E753C4.7030903@rabbit.us> <47E7C609.9000501@bteam.hu> <47E7CBD9.4020900@rabbit.us> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <47E7CBD9.4020900@rabbit.us> Sender: linux-raid-owner@vger.kernel.org To: Peter Rabbitson , linux-raid@vger.kernel.org List-Id: linux-raid.ids hi > The validity of the snipped arguments depends on how many devices you > have at every level: > > *) how many nodes there are? 8 nodes > *) how many disks per node? do all nodes have an equal amount of disks? currently there are 5 disks at every node, and yes: all nodes have equal amount, but the only thing that matters is that the exported size should be the same > > Without additional info I would say this: The problem with using raid5 > on the top node is that you are stressing your network additionally > for every r-m-w-cycle. Also rebuild of this array, especially if you > add more leaves will be more and more resource intensive. after the new nics installed, i except that the rebuild would take about 8 hours to complete yes, the r-m-w-cycle would be a pain - but i expect to have much more reads than writes this is truly resource intensive - but the bottleneck would be not at the network level, i think it will be at the root node's south-west connection i must note that this is my first raid setup ;) and i've not faced with rmw-cycle problems before, and because the use conditions doesn't imply continous random writes - we will be happy with this, next week we will try it out in target conditions - and if something is not going as expect, i will reconsider applying raid10 to it > In contrast if the top array is RAID10 with 2 chunk copies, you will > sacrifice half the space, however your rebuild will utilize only 2 > drives (one reader one writer). yes, that clearly could reach better performance, with .5 usable space-ratio i'm working with relatively low-budget current ratio is: 4*7/(5*8) = .7 kirk