Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
That's very clear thanks for your input Lars! Regards, Myles ________________________________________ From: drbd-user-bounces at lists.linbit.com [drbd-user-bounces at lists.linbit.com] on behalf of Lars Ellenberg [lars.ellenberg at linbit.com] Sent: 09 October 2013 19:39 To: drbd-user at lists.linbit.com Subject: Re: [DRBD-user] Another iSCSI Active/Active Thread On Wed, Oct 09, 2013 at 03:33:51PM +0000, Myles Gray wrote: > I know that this has been discussed many times over by the community > and Linbit engineers, however, is iSCSI active/active now safely > deployable on DRBD using the built in kernel scsi target (LIO)? > > I ask because it now supports VMWare's VAAI which is nothing more than > a collection of t10 SCSI commands (it's not an API at all, why they > called it that I don't know): > > 0x93 WRITE SAME(16) > 0x41 WRITE SAME(10) > 0x42 UNMAP > 0x89 SCSI COMPARE and WRITE - ATS > 0x83 EXTENDED COPY > > The SCSI COMPARE AND WRITE command is used by clustering aware > applications for resource locking, for example ESXi - therefore if > your initiator is ESX's iSCSI Initiator and your target (LIO) supports > VAAI then you can run active/active iSCSI on DRBD with no problems? The basic problem is that targets keep state (iSCSI is not stateless). But that state is neither communicated nor coordinated between multiple such targets in any fashion (or I missed some recent development). Which is why things *will* break if you want to talk to two independend such targets concurrently. (Even though you can likely build setups that will *appear* to work for a long time -- in fine weather). Whether or not those target implementations learn to support additional features is unrelated to this particular problem. The capabilities and features of *one* single target implementation have absolutley nothing to do with the fact that you want to talk to *two* independend such targets, concurrently. And they don't know and don't care about each other. It does not help that the target now supports commands that can be used by cluster aware applications. If you want to use multiple targets concurrently on the same data set in a cluster, the target needs to become cluster aware *itself*. Whether or not the backend storage is replicated by DRBD, shared SCSI or SAN, or whatever else, is unrelated as well. -- : Lars Ellenberg : LINBIT | Your Way to High Availability : DRBD/HA support and consulting http://www.linbit.com DRBD® and LINBIT® are registered trademarks of LINBIT, Austria. __ please don't Cc me, but send to list -- I'm subscribed _______________________________________________ drbd-user mailing list drbd-user at lists.linbit.com http://lists.linbit.com/mailman/listinfo/drbd-user