From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?UTF-8?Q?Mathias_Bur=C3=A9n?= Subject: Re: External bitmap, questions Date: Sat, 19 Feb 2011 12:20:41 +0000 Message-ID: References: <20110219154924.2218c87c@notabene.brown> <20110219171437.3a6200e6@natsu> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20110219171437.3a6200e6@natsu> Sender: linux-raid-owner@vger.kernel.org To: Roman Mamedov Cc: NeilBrown , Linux-RAID List-Id: linux-raid.ids On 19 February 2011 12:14, Roman Mamedov wrote: > On Sat, 19 Feb 2011 04:55:32 +0000 > Mathias Bur=C3=A9n wrote: > >> > External bitmaps use 'BMAP' to find where the file lives on the de= vice and >> > then writes directly to the device - not through the filesystem. >> > >> > So as long as there is no tail-packing to block migration happenin= g it >> > should work fine. >> > >> > I haven't looked inside ext4 but I am fairly confident that extern= al >> > bitmaps will work properly. >> > >> > NeilBrown >> > >> > >> >> Thanks, Neil. Are there any differences between using an internal or >> external bitmap? Also, does one need a bitmap at all when not planni= ng >> to "mess" with the array? (does it provide any other purpose?) > > I have successfully stored an external bitmap on XFS for a brief time= =2E > However it proved difficult to ensure that the device storing the bit= map is > mounted, accessible and writable prior to boot scripts attempting to = run the md > arrays, so since then I just switched to an internal bitmap. The nega= tive > performance it had can be minimized to almost zero by using a larger = bitmap > chunk size. > > -- > With respect, > Roman > I ended up storing the bitmap on my root filesystem (ext4) for now. It's currently at the default size but I think I'll recreate it with 64MB size. // Mathias -- 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