From mboxrd@z Thu Jan 1 00:00:00 1970 From: Piergiorgio Sartor Subject: Re: Roadmap for md/raid ??? Date: Mon, 19 Jan 2009 19:19:19 +0100 Message-ID: <20090119181919.GB4290@lazy.lzy> References: <18763.7881.300921.177207@notabene.brown> <20090111181413.GA24988@lazy.lzy> <18803.55804.905420.503480@nbeee.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <18803.55804.905420.503480@nbeee.brown> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hi, > > RAID-5/6 with heterogeneous devices. [...] > I've thought about this occasionally but don't think much of the idea. > It seems nice until you think about what happens when devices fail > and you need to integrate hot spares. > Clearly any spare will need to be as big as the largest device. > When that get integrated in place of a small device, you will be > wasting space on it, and then someone will want to be able to > grow the array to use that extra space, which would be rather > messy. > > I think it is best to assume that all devices are the same size. > Trying to support anything else in a useful way would just add > complexity with little value. I see your point and I also agree that complexity might be too much. Nevertheless I disagree about the "wasting space", since I can see a scenario where there is even more wasting. Let's assume we have a RAID-5 with 7 disks. Each time an HD fails, we will replace it with a larger one, since this will be cheaper. Once we replaced 3 HDs, with could use the unused space in RAID-5 again. Unfortunately, with the current features, we will have to wait to fail all the 7 disks. So, with 6 HDs replaced with larger ones, we will have a lot of wasted space. Of course, unless we did a clever partitioning at very the beginning. But again, I do agree the complexity might not pay off the advantages, maybe better the "clever partitioning". Thanks, bye, -- piergiorgio