<div>Hi Malahal,</div> <div> </div> <div> </div> <div><span class="gmail_quote">2009/7/27, <a href="mailto:malahal@us.ibm.com">malahal@us.ibm.com</a> <<a href="mailto:malahal@us.ibm.com">malahal@us.ibm.com</a>>:</span> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">brem belguebli [<a href="mailto:brem.belguebli@gmail.com">brem.belguebli@gmail.com</a>] wrote:<br>> Hi,<br> > I have a few questions concerning LVM mirror implementation, and I<br>> couldn't find any suitable design doc<br>> I need to setup a dual site ( a few miles between the 2 sites, around 1 ms<br>> RTD) mirror based cluster system.<br> <br>You need asynchronous mirroring (remote replication module). This is not<br>in mainline (not sure if included in the latest RHEL release). The<br>following comments apply to dm-mirror module that is already in the<br> mainline.</blockquote> <div> </div> <div>Do you mean a Disk array based replication mechanism (SRDF, CA, etc...)? or is it system based , and if so do you have any technical document link to provide me ?</div> <div> </div><br> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">> - *what is the default behaviour of the mirroring, writing in parallel to<br>> both mirror legs or serialized ? what about read requests ?<br> <br>It writes in parallel. Reads from a single device (switches on a device<br>failure only).<br><br>> - for write requests, is the ack returned to the application (thru VFS)<br>> when the 2 legs are updated or only when the first is updated ?<br> <br>When two are updated. (you need 'remote replication' module for the<br>latter behaviour)</blockquote> <div>As I said, I couldn't find suitable doc about this, and in fact that's the behaviour I'm expecting (acking only when the 2 legs are up to date) . Can you point me to the good doc ?</div> <div> </div><br> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">> - Is there a way to control it ?<br><br> I don't think so.<br><br>> - what happens if the log device is lost ?<br> <br>The mirror stops and a daemon re-allocates the log and the mirror should<br>be back to business (this depends on your lvm configuration though).</blockquote> <div> </div> <div>As the mirrorlog is in my case bound to a given SAN device (let's say /dev/sdx) and this device belongs to the SAN array located on the datacenter that experienced a disaster, my mirror won't be able to be brought back online as long as /dev/sdx is down .</div> <br> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">> I saw a post about LVM mirror vs mdadm where it is about the location of<br>> the mirror log<br> > ([1]<a href="https://www.redhat.com/archives/linux-lvm/2009-July/msg00012.html">https://www.redhat.com/archives/linux-lvm/2009-July/msg00012.html</a>)<br>> someone gave the answer that when creating the LV's with --alloc anywhere<br> > it will auto locate the log on any of the PV's.<br>> According to what I could read, the --alloc doesn't intend for that, am I<br>> right ?<br><br>Replace your "auto locate" to "allocate the log on any of the PV's".<br> <br>What is the intention of the "--alloc anywhere" from your reading?</blockquote> <div> </div> <div>According to the lvm man page, --alloc anywhere, in crontrary to --alloc strict (default) would allocate "data" LE to any pv forming the VG, resulting in having striped or mirrored LE on the same PV (sic!).</div> <div> </div> <div>It doesn't seem to concern log device which is de facto a 3rd device not necessary belonging to the VG, or the man page is not up2date.</div> <div> </div><br> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">--Malahal.<br><br>_______________________________________________<br>linux-lvm mailing list<br><a href="mailto:linux-lvm@redhat.com">linux-lvm@redhat.com</a><br> <a href="https://www.redhat.com/mailman/listinfo/linux-lvm">https://www.redhat.com/mailman/listinfo/linux-lvm</a><br>read the LVM HOW-TO at <a href="http://tldp.org/HOWTO/LVM-HOWTO/">http://tldp.org/HOWTO/LVM-HOWTO/</a><br> </blockquote></div><br>