On Tue, 2006-04-25 at 16:13 -0600, Ty! Boyack wrote: > The first scenario you give is most likey the one to occur. I'm > thinking the server is active, has active volumes which use the iSCSI > array as PVs, and may or may not have applications accessing it at the > time of the failure. I'm glad to hear that the other volumes should be > accessable (assuming we don't stripe across the devices). It also makes > sense that the user will get a r/w error or i/o error. maybe u can consider a raid5 on top of these iscsi disks, if u app are very unhappy or buggy to see these r/w errors. > > I'm still wondering if the disk comes back if the LV will be available > again, or if LVM will mark it as failed, and assume that all blocks on it will not automatically available i think, but with that "echo ...", u might be able to see it again. > it are invalid now and forevermore. Or is this a function of the > filesystem? I'll be building a test case and will certainly have fun > breaking it like this. I'm glad to know of the ability to test it as > Jonathan pointed out that will be a simpler test bed. keep us updated. thanks. > > Good info - thanks folks! > > -Ty! > > Ming Zhang wrote: > > >assume 2 scenarios > > > >1) this PV is under use when it is disconnected temporarily. then > >eventually will return r/w errors to applications. but other LVs are > >still accessible. > > > >2) system is off and boot up again. for this system will complain PV > >with UUID ... is not found. so the only way is to partially activate VG. > > > >am i correct here? > > > >ming > > > > > > > >On Tue, 2006-04-25 at 15:21 -0500, Jonathan E Brassow wrote: > > > > > >>It is simple to play with this type of scenario by doing: > >> > >>echo offline > /sys/block/<sd dev>/device/state > >> > >>and later > >> > >>echo running > /sys/block/<sd dev>/device/state > >> > >>I know this doesn't answer your question directly. > >> > >> brassow > >> > >> > >>On Apr 25, 2006, at 2:57 PM, Ming Zhang wrote: > >> > >> > >> > >>>my 2c. fix me if i am wrong > >>> > >>>either activate the VG partially, and then all LVs on other PVs are > >>>still accessible. I remember these LVs will only have RO access. Though > >>>I have no idea why. > >>> > >>>use dm-zero to generate a fake PVs and add to VG, then allow VG to > >>>activate and access those LV. But i do not know if you access a LV that > >>>is partially or fully on this PV, what will happen. > >>> > >>>Ming > >>> > >>> > >>>On Tue, 2006-04-25 at 13:08 -0600, Ty! Boyack wrote: > >>> > >>> > >>>>I've been intrigued by the discussion of what happens when a PV fails, > >>>>and have begun to wonder what would happen in the case of a transient > >>>>failure of a PV. > >>>> > >>>>The design I'm thinking of is a SAN environment with several > >>>>multi-terabyte iSCSI arrays as PVs, being grouped together into a > >>>>single > >>>>VG, and then carving LVs out of that. We plan on using the CLVM tools > >>>>to fit into a clustered environment. > >>>> > >>>>The arrays themselves are robust (RAID 5/6, redundant power supplies, > >>>>etc.) and I grant that if we lose the actual array (for example, if > >>>>multiple disks fail), then we are in the situation of a true and > >>>>possibly total failure of the PV and loss of it's data blocks. > >>>> > >>>>But there is always the possiblity that we could lose the CPU, memory, > >>>>bus, etc. in the iSCSI controller portion of the array, which will > >>>>cause > >>>>downtime, but no true loss of data. Or someone may hit the wrong > >>>>power > >>>>switch and just reboot the thing, taking it offline for a short time. > >>>>Yes, that someone would probably be me. Shame on me. > >>>> > >>>>The key point is that the iSCSI disk will come back in a few > >>>>minutes/hours/days depending on the failure type, and all blocks will > >>>>be > >>>>intact when it comes back up. I suppose the analagous situation would > >>>>be using LVM on a group of hot swap drives and pulling one of the > >>>>disks, > >>>>waiting a while, and then re-inserting it. > >>>> > >>>>Can someone please walk me through the resulting steps that would > >>>>happen > >>>>within LVM2 (or a GFS filesystem on top of that LV) in this situation? > >>>> > >>>>Thanks, > >>>> > >>>>-Ty! > >>>> > >>>> > >>>> > >>>_______________________________________________ > >>>linux-lvm mailing list > >>>linux-lvm@redhat.com > >>>https://www.redhat.com/mailman/listinfo/linux-lvm > >>>read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ > >>> > >>> > >>> > >>_______________________________________________ > >>linux-lvm mailing list > >>linux-lvm@redhat.com > >>https://www.redhat.com/mailman/listinfo/linux-lvm > >>read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ > >> > >> > > > >_______________________________________________ > >linux-lvm mailing list > >linux-lvm@redhat.com > >https://www.redhat.com/mailman/listinfo/linux-lvm > >read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ > > > > > > _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
