Date: Thu, 30 Sep 2004 21:42:13 -0400 From: Allan Fields <bsd@afields.ca> To: Jo?o Carlos Mendes Lu?s <jonny@jonny.eng.br> Cc: Ivan Voras <ivoras@fer.hr> Subject: Re: GEOM (ggate) compression consumer +problem Message-ID: <20041001014213.GN47410@afields.ca> In-Reply-To: <415C9967.3090309@jonny.eng.br> References: <415BDFC2.1020304@fer.hr> <415C9967.3090309@jonny.eng.br>
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The funny thing is you'll run into lots of these types of similarities in solutions between the two levels (at the VFS and at the device level). The parallel solutions may differ significantly in implementation, but are layer-wise homologies (analogs). You can do compression and encryption at multiple levels in the system w/ various benefits and disadvantages. Data can pass through any of these layers on it's way to disk or over the network as the case might be. On Thu, Sep 30, 2004 at 08:40:23PM -0300, Jo?o Carlos Mendes Lu?s wrote: > Instead of block compression, wouldn't it be better (and maybe easier) > to use file compresion, in a VFS layer (and a threaded daemon)? No need to have a user-side daemon if the compression/encryption logic is implemented on the kernel side. Else you may run into bottlenecks and other implementation issues. One alternative is to implement a VFS infrastructure like DragonFly has planned to allow user-side filesystems to become practical. There are arguments about why each approach should be used. > A real useful VFS layer would have an option to compress only rarely > used files. And keep the real layer accessible, to allow dumping of > compressed backend files. > > Also, an option to encrypt the backend files could be useful. > Encrypting after compressing is always better. You're referring to capabilities that FiST (http://www.filesystems.org) can offer. Support for FreeBSD SCA isn't yet complete which is required to get compression (gzipfs) to work. > This is what I would like to see in a compressed file system. While the granularity of operation is reduced to the file level by sticking with a VFS layer implementation, it can be more complicated than device level compression/encryption at this point and there are a few issues remaining to be solved. > Ivan Voras wrote: > >I've made a GEOM compression layer daemon for ggate (compresses data > >before storing to underlying file/media). It's still early version and > >unfinished, and it's available at: > > > >http://ivoras.sharanet.org/ggcomp.tgz > > Jonny > > -- > Jo?o Carlos Mendes Lu?s - Networking Engineer - jonny@jonny.eng.br -- Allan Fields, AFRSL - http://afields.ca 2D4F 6806 D307 0889 6125 C31D F745 0D72 39B4 5541
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