Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
>-----Original Message----- >From: Adam Goryachev [mailto:mailinglists at websitemanagers.com.au] >Sent: Friday, March 01, 2013 11:16 AM >To: Jason Thomas >Cc: Dan Barker; drbd List (drbd-user at lists.linbit.com) >Subject: Re: [DRBD-user] drbd pacemaker scst/srp 2 node active/passive question > >> ----- Original Message ----- >> From: "Dan Barker" <dbarker at visioncomm.net> >> To: "drbd List (drbd-user at lists.linbit.com)" <drbd-user at lists.linbit.com> >> Sent: Friday, March 1, 2013 4:59:40 AM >> Subject: Re: [DRBD-user] drbd pacemaker scst/srp 2 node active/passive question >> >> That's easy, I've been doing it for years, going back to ESXi 4.1 at least, maybe even to 4.0. I run ESXi 5.1 now. >> >> Set up both the servers in ESXi, Configuration, Storage adapters. Use static discovery, because you can list the targets whether they exist or not. When the primary goes down, the secondary will come up (if it's available) on ESXi without intervention. >> >> In my setup, the .46 drbd is secondary, and invisible to ESXi. .47 is primary and visible to ESXi. I run the following targets (you can do this with the GUI, but I get lazy): >> >> vmkiscsi-tool -S -a "172.30.0.46 iqn.2012-05.com.visioncomm.DrbdR:Storage03" vmhba39 >> vmkiscsi-tool -S -a "172.30.0.46 iqn.2012-06.com.visioncomm.DrbdR:Storage02" vmhba39 >> vmkiscsi-tool -S -a "172.30.0.46 iqn.2012-08.com.visioncomm.DrbdR:Storage01" vmhba39 >> vmkiscsi-tool -S -a "172.30.0.46 iqn.2012-08.com.visioncomm.DrbdR:Storage00" vmhba39 >> vmkiscsi-tool -S -a "172.30.0.47 iqn.2012-05.com.visioncomm.DrbdR:Storage03" vmhba39 >> vmkiscsi-tool -S -a "172.30.0.47 iqn.2012-06.com.visioncomm.DrbdR:Storage02" vmhba39 >> vmkiscsi-tool -S -a "172.30.0.47 iqn.2012-08.com.visioncomm.DrbdR:Storage01" vmhba39 >> vmkiscsi-tool -S -a "172.30.0.47 iqn.2012-08.com.visioncomm.DrbdR:Storage00" vmhba39 >> >> If both are primary, I see 4 targets, 8 paths. This "never<g>" happens. Usually, I see 4 targets, 4 paths. >> >> I always do the switchover manually, so you might see slightly different results. My steps are: >> >> Go primary on the .46 server. >> >> Start the target (iscsi-target) software on the .46 server. >> >> Rescan on all ESXi. >> >> Stop the target software on the .47 server (ESXi fails over to the other path seamlessly at this point). >> >> Stop drbd on .47 and do whatever maintenance was necessary. >> >> To reverse: >> >> The same steps, but you can skip the scan if the ESXi have "seen" both targets since boot. One shows up as active and the other shows up as dead, but the VMs don't care. >Question: Given the above, at some point, you have dual primary, and >iscsi-target on both nodes for a short period of time. Is there actually >a problem to run like this all the time? Regardless of which DRBD node >is written, DRBD should ensure it is copied to the other node. Also, >reads should not be relevant since it doesn't matter which DRBD node the >data comes from. > >However, I'm not so confident to actually try this, especially if it >will break in some subtle and horrible way by corrupting the data slowly >over a period of 6 months etc... > >Thanks, >Adam When ESXi discovers the additional paths, it does not immediately use them. It remains using the original path for Active I/O. Yes, it's dual primary, and yes there is an exposure if multiple ESXi address the same target with different paths. But, until/if the first path goes down, no I/O occurs on the other path. Only running dual primary for a minute or so maybe once or twice a year has not shown me any issues, but they are certainly possible. Dan