Kyle McDonald wrote: > David Magda wrote: > >> Quite often swap and dump are the same device, at least in the >> installs that I've worked with, and I think the default for Solaris >> is that if dump is not explicitly specified it defaults to swap, yes? >> Is there any reason why they should be separate? >> >> >> > I beleive there are technical limitations with ZFS Boot that stop them > from sharing the same Zvol.. > Yes, there is. Swap zvols are ordinary zvols which still COW their blocks and leverage checksumming, etc. Dump zvols don't have this luxury because when the system crashes you are limited in the number of tasks that you can perform. So we solved this by changing the personality of a zvol when it's added as a dump device. In particular, we needed to make sure that all the blocks that the dump device cared about were available at the time of a system crash. So we preallocate the dump device when it gets created. We also follow a different I/O path when writing to a dump device allowing us to behave as if we were a separate partition on the disk. The dump subsystem doesn't know the difference which is exactly what we wanted. :-)
>> Having two just seems like a waste to me, even with disk sizes being >> what they are (and growing). A separate dump device is only really >> needed if something goes completely wrong, otherwise it's just >> sitting there "doing nothing". If you're panicing, then whatever is >> in swap is now no longer relevant, so over writing it is no big deal. >> >> > That said, with all the talk of dynamic sizing, If, during normal > operation the swap Zvol has space allocated, and the Dump Zvol is sized > to 0. Then during a panic, could the swap volume be sized to 0 and the > dump volume expanded to whatever size. > Unfortunately that's not possible for the reasons I mentioned. You can resize the dump zvol to a smaller size but unfortunately you can't make it a size 0 as there is a minimum size requirement. Thanks, George > This at least while still requireing 2 Zvol's would allow (even when the > rest of the pool is short on space) a close approximation of the old > behavior of sharing the same slice for both swap and dump. > > -Kyle > > >> _______________________________________________ >> zfs-discuss mailing list >> zfs-discuss@opensolaris.org >> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss >> >> > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
