From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Clements Subject: Re: enhancements to the raid1 driver Date: Mon, 17 Feb 2003 15:09:16 -0500 Sender: linux-raid-owner@vger.kernel.org Message-ID: <3E51416C.2E7E92D@SteelEye.com> References: <3E4D96DB.7AC5954B@SteelEye.com> <15952.20020.858737.543347@notabene.cse.unsw.edu.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: To: Neil Brown Cc: linux-raid@vger.kernel.org, jejb@SteelEye.com List-Id: linux-raid.ids Neil, Neil Brown wrote: > Maybe if you explain more about what would be the specifics of these > ioctls that you want to pass down. Sure, no problem... > > asynchronous replication - to get acceptable performance when the backup > > leg of the raid1 mirror is slow (e.g., nbd over a LAN or WAN) > > Hmmm. I cannot figure out exactly what would be asynchronous... Nor > can I see how this would require an ioctl. Basically, we're trying to overcome latency penalties associated with writing data and waiting for acknowledgements over a network (or any other slow transport). So, all writes to the backup device(s) would be queued, so that the writes could take place asynchronously. The size of the queue and whether or not to enable this asynchronous mode would be user-configurable; that's where the ioctls come in. Since user configuration of the md driver is currently done with ioctls, this seemed like the natural choice. Of course, I'm open to other suggestions, if there's a better way to do this... -- Paul