From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: How to handle >16TB devices on 32 bit hosts ?? Date: Sat, 18 Jul 2009 09:48:11 +0200 Message-ID: <20090718074811.GA2682@basil.fritz.box> References: <19041.4714.686158.130252@notabene.brown> <20090718043155.GI4231@webber.adilger.int> <871voewm6y.fsf@basil.nowhere.org> <20090718065213.GK4231@webber.adilger.int> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andi Kleen , device-mapper development , Neil Brown , linux-fsdevel@vger.kernel.org, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org To: Andreas Dilger Return-path: Content-Disposition: inline In-Reply-To: <20090718065213.GK4231@webber.adilger.int> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Sat, Jul 18, 2009 at 02:52:13AM -0400, Andreas Dilger wrote: > If you aren't running a 32-bit system with this config, you shouldn't > really care. For those systems that need to run in this mode they > would rather have it work a few percent slower instead of not at all. Well, it doesn't work at all anyways due to the fsck problem. > The last test numbers I saw were 5GB of RAM for a 20TB filesystem, > but since the bitmaps used are fully-allocated arrays that isn't > surprising. We are planning to replace this with a tree, since the > majority of bitmaps used by e2fsck have large contiguous ranges of > set or unset bits and can be represented much more efficiently. You would need to get <~2.5GB for 32bit. In practice that's the limit you have there. > Also, for filesystems like btrfs or ZFS the checking can be done > online and incrementally without storing a full representation of > the state in memory. You could, but I suspect it would be cheaper to just use a 64bit system than to rewrite fsck. 64bit is available for a lot of embedded setups these days too. -Andi -- ak@linux.intel.com -- Speaking for myself only.