From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ryusuke Konishi Subject: Re: Split some metadata onto separate device? Date: Wed, 08 Jun 2011 21:48:52 +0900 (JST) Message-ID: <20110608.214852.237935973.ryusuke@osrg.net> References: <201106031229.38758.dexen.devries@gmail.com> <20110604.022621.01482278.ryusuke@osrg.net> <201106031942.29133.dexen.devries@gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <201106031942.29133.dexen.devries-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-nilfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: Text/Plain; charset="us-ascii" To: dexen.devries-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org Cc: linux-nilfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Fri, 3 Jun 2011 19:42:28 +0200, dexen deVries wrote: > Hi Ryusuke, > > > On Friday 03 June 2011 19:26:21 you wrote: > > (...) > > NILFS2 is a log-structured filesystem and that means the filesystem > > itself is a big journal. My understanding is using separate journal > > device has no merit of performance. > > > > On the other hand, We may be able to speed up the filesystem by > > putting DAT (disk address translation) metadata to a separate device. > > I mean putting a full copy of the DAT metadata on the sperate device > > instead of journal of it. > > *nods* sounds interesting. Of course changing on-disk format would hurt ;-) > > > > But, I think we have other approaches to think about before that with > > regard to performance improvement. For example, applying "extent" to > > DAT seems much more effective. > > Currently every block of file gets own entry in DAT, right? Exactly. > By the way, it seems to me that the in-kernel GC does not attempt to > de- fragment files. Is that the case? If so, would probably mean > extents would not help very much for fragmented files. Also, on > magnetic media, a lot of seeking happens in case of fragmented > files. Yes, but extents will decrease the amount of metadata, and this has potential for speed up. NILFS2 uses 32 bytes metadata per disk block at present. I guess you know that the number of DAT blocks are actually indispensable through analysis using the dumpseg tool. Regards, Ryusuke Konishi > Regards, > -- > dexen deVries > > ``One can't proceed from the informal to the formal by formal means.'' > -- > To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in > the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html