From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Zhang Subject: Re: Device Mapper as a cache for SAN? Date: Mon, 10 Apr 2006 20:35:44 -0400 Message-ID: <1144715744.8591.197.camel@localhost.localdomain> References: <20060410184531.GA12908@www.ewilts.org> <1144704325.8591.170.camel@localhost.localdomain> Reply-To: mingz@ele.uri.edu, device-mapper development Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Eric Van Hensbergen Cc: device-mapper development List-Id: dm-devel.ids On Mon, 2006-04-10 at 19:28 -0500, Eric Van Hensbergen wrote: > On 4/10/06, Ming Zhang wrote: > > On Mon, 2006-04-10 at 14:46 -0500, Eric Van Hensbergen wrote: > > > On 4/10/06, Ed Wilts wrote: > > > > > > > > The obvious question is why? What would this provide that the kernel > > > > and file systems don't already provide? > > > > > > > > > > Well, kernel provides in-memory page cache, not local disk page cache. > > > There is some ongoing remote file system local disk cache work being > > > done, but it applies primarily to AFS and NFS - not block-based > > > transports such as iSCSI and AOE. The various cluster file systems > > > may provide something more akin to this, but again, this doesn't > > > really cover SAN technologies -- not in any sort of a generic way. > > > Let me know if I'm missing something. > > > > still, what is the main benefit of this cache? what u mean "local disk > > page cache"? use "local disk" as page cache or page cache for "local > > disk" or something else? > > > > Okay, I suppose I wasn't exactly clear. What I want is something that > will let me use a local disk (or local disks) as a cache for a storage > area network volume (or volumes). There are a variety of scenarios - so a disk as cache for another (remote) disk(s). > my primary interest is in using it for large clusters with shared > read-only volumes or with exclusive-access read/write volumes. So, > local disk page cache is probably not the right terminology -- it is > simply a local block cache for a remote block device. yes, "page cache" has its meaning in linux. as i know, no stable implementation for this. > > -eric