On 3/24/10 4:35 PM, "Mark Post" <[email protected]> wrote: >>>> On 3/24/2010 at 03:20 PM, David Boyes <[email protected]> wrote: >> CLVM still doesn't >> handle the MW minidisk case correctly > > In what way? Is it something that's fixable from Linux, or is it z/VM > specific? (Gotta know what to tell people when this comes up, because clearly > it will.)
A little bit of both. For this to work properly (IMHO), you need to limit it to link mode MWV (so that CP observes and respects virtual reserve/release). For integrity reasons (again IMHO), cLVM should not permit shared access if the disk device does not respond correctly to reserve/release (because it wouldn't work with real reserve/release in LPARs either) or the appropriate analogue for other platforms. If it doesn't, you're cruising for data corruption, and there's enough opportunities for stupid configuration errors now, no need to enable any more. Second, it needs to reliably use reserve/release if it's present. Looks like the designer completely implemented the FCP case (easy, since it's basically the same on Intel), but the non-FCP case has several problems that cause the reserve/release CCWs not to be reliably issued or cleared with n>5 hosts. Don't know why 5 is magic, but it worked OK with 4, failed and corrupted data repeatably with 6, sometimes failed with 5. Maybe load or timing related. Third, it also doesn't anticipate a very large number of possible guests sharing a disk, such as in a z/VM environment (there are a few artificial limits that seem to be introduced from the FCP case that shouldn't exist for the non-FCP case). The code wasn't written with a massively shared resource environment like z/VM in mind; no fault for that, but that feature will probably see more use in this environment than anywhere else, so we might as well be ahead of the game and fix it now. I submitted patches upstream to various pieces involved in the problem. Probably nothing you need to do now, other than make sure that MWV is the recommended basis for this kind of crazyness in a z/VM environment. -- db ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
