Re: [zfs-discuss] query re disk mirroring
On 29/11/2012 14:51, Edward Ned Harvey (opensolarisisdeadlongliveopensolaris) wrote: From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- boun...@opensolaris.org] On Behalf Of Enda o'Connor - Oracle Ireland - Say I have an ldoms guest that is using zfs root pool that is mirrored, and the two sides of the mirror are coming from two separate vds servers, that is mirror-0 c3d0s0 c4d0s0 where c3d0s0 is served by one vds server, and c4d0s0 is served by another vds server. Now if for some reason, this physical rig loses power, then how do I know which side of the mirror to boot off, ie which side is most recent. If one storage host goes down, it should be no big deal, one side of the mirror becomes degraded, and later when it comes up again, it resilvers. If one storage host goes down, and the OS continues running for a while and then *everything* goes down, later you bring up both sides of the storage, and bring up the OS, and the OS will know which side is more current because of the higher TXG. So the OS will resilver the old side. If one storage host goes down, and the OS continues running for a while and then *everything* goes down... Later you bring up only one half of the storage, and bring up the OS. Then the pool will refuse to mount, because with missing devices, it doesn't know if maybe the other side is more current. As long as one side of the mirror disappears and reappears while the OS is still running, no problem. As long as all the devices are present during boot, no problem. Only problem is when you try to boot from one side of a broken mirror. If you need to do this, you should mark the broken mirror as broken before shutting down - Certainly detach would do the trick. Perhaps offline might also do the trick. thanks, from my testing,ie appears that if disk goes into UNAVAIL state and further data is written to the other disk, then even if I boot from the stale side of mirror, the boot process detects this and actually mounts the good side and resilvers the side I passed to boot arg. If disk is FAULTED then booting from it results in the zfs panicing and telling me to boot the other side. So it appears that some failure modes are handled well, others appear to result in the panic loop. I have both sides in boot-device and both disks are available to OBP at boot time in my testing. I'm just trying to determine optimal value for autoboot in my ldoms guests in the face of various failure modes. thanks for the info Enda Does that answer it? ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
[zfs-discuss] query re disk mirroring
Hi Say I have an ldoms guest that is using zfs root pool that is mirrored, and the two sides of the mirror are coming from two separate vds servers, that is mirror-0 c3d0s0 c4d0s0 where c3d0s0 is served by one vds server, and c4d0s0 is served by another vds server. Now if for some reason, this physical rig loses power, then how do I know which side of the mirror to boot off, ie which side is most recent. As an example ( contrived now mind you ) I shutdown the IO server domain serving c3d0s0, I then copy a large file into my root pool ( goes to vds serving c4d0s0 ), then shut down the guest and the other service domain gracefully, then boot guest off c3d0s0 ( have restarted the service domain there ), the large file is obviously missing now. Is there any way if the guest is stopped, that I can know which side of the mirror to boot off that was most recent? Enda ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] query re disk mirroring
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- boun...@opensolaris.org] On Behalf Of Enda o'Connor - Oracle Ireland - Say I have an ldoms guest that is using zfs root pool that is mirrored, and the two sides of the mirror are coming from two separate vds servers, that is mirror-0 c3d0s0 c4d0s0 where c3d0s0 is served by one vds server, and c4d0s0 is served by another vds server. Now if for some reason, this physical rig loses power, then how do I know which side of the mirror to boot off, ie which side is most recent. If one storage host goes down, it should be no big deal, one side of the mirror becomes degraded, and later when it comes up again, it resilvers. If one storage host goes down, and the OS continues running for a while and then *everything* goes down, later you bring up both sides of the storage, and bring up the OS, and the OS will know which side is more current because of the higher TXG. So the OS will resilver the old side. If one storage host goes down, and the OS continues running for a while and then *everything* goes down... Later you bring up only one half of the storage, and bring up the OS. Then the pool will refuse to mount, because with missing devices, it doesn't know if maybe the other side is more current. As long as one side of the mirror disappears and reappears while the OS is still running, no problem. As long as all the devices are present during boot, no problem. Only problem is when you try to boot from one side of a broken mirror. If you need to do this, you should mark the broken mirror as broken before shutting down - Certainly detach would do the trick. Perhaps offline might also do the trick. Does that answer it? ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
