From: Goswin von Brederlow Subject: Re: ext4 64bit (disk >16TB) question Date: Tue, 15 Jul 2008 23:03:31 +0200 Message-ID: <87mykirhb0.fsf@frosties.localdomain> References: <87bq10w8gv.fsf@frosties.localdomain> <20080715132734.68c64000@ichigo> <20080715195116.GL6239@webber.adilger.int> <487D0572.50503@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andreas Dilger , "Jose R. Santos" , Goswin von Brederlow , linux-ext4@vger.kernel.org To: Ric Wheeler Return-path: Received: from fmmailgate03.web.de ([217.72.192.234]:54821 "EHLO fmmailgate03.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754306AbYGOVDf (ORCPT ); Tue, 15 Jul 2008 17:03:35 -0400 In-Reply-To: <487D0572.50503@gmail.com> (Ric Wheeler's message of "Tue, 15 Jul 2008 16:15:46 -0400") Sender: linux-ext4-owner@vger.kernel.org List-ID: Ric Wheeler writes: > Andreas Dilger wrote: >> Jose, >> while waiting for the "efficient bitmap" support, how hard would it be >> to implement "inefficient bitmaps" that just malloc some GB of memory >> if needed? This would at least allow people with huge devices to test >> mke2fs/ext4/e2fsck in the meantime. >> >> Cheers, Andreas >> -- >> Andreas Dilger >> Sr. Staff Engineer, Lustre Group >> Sun Microsystems of Canada, Inc. >> >> > > I think that would be very useful - how much DRAM would we need for a > 16TB file system ;-) ? > > ric The patched 1.39 e2fsprogs managed to format a 16TIB under kvm with 1GiB ram and 128k swap. A 32TiB disk format uses nearly 1GiB ram for mkfs alone and eventualy managed to deadlock the I/O layer in kvm with 1.5GB ram and 128k swap. (Something I'm sure is kvms fault. :) But fsck is suposed to eat more by a factor (see other mails in thread). So having 4-16GiB ram is probably recommended for anyone thinking about testing. I used the sparse_create script linked on one of the ext4 wiki pages with a sparse loopback file and used mke2fs -i $((64*1024*1024)) to speed up things. With that a 16TiB ext4 uses somewhat over 4GiB freshly formated. MfG Goswin