gmirror (was Re: It's time to bite the bullet and do a major upgrade...)
On Wednesday 15 November 2006 16:58, John Nielsen wrote: It is possible to convert regular devices into gmirror members after they have data on them, but unless you're extremely careful there's a small risk of the gmirror metadata sector overlapping a data sector. OK, I see the warning in the gmirror(8) manpage that gmirror metadata overwrites the last sector of the provider. Is that sector more likely, or less likely, to be in use than any other sector on a non-full disk? If it's equally or less likely the risk is extremely small - which I know is no consolation when it happens! In this case, I'm doing something of a ``stunt upgrade'' anyway: I have two remote boxes to upgrade to 6.1, one of which is running 5.4-RELEASE and one 4.8-RELEASE. Both boxes have 80GB drives, and on my last flying visit I added to each box a blank 80GB drive and a null-modem serial link to a neighbouring ssh-accessible box. The plan is to ssh to the neighbour box, establish a serial console on the upgrade target, install 6.1 from scratch over the network on the blank drive and then make it the only drive in a gmirror. Once that's done, data can be migrated from the original drive, which can then be added to the mirror. I have successfully carried out the procedure on a box in my office (so that I could intervene when it all went horribly wrong, several times) and am in the process of documenting it: as I said earlier, I couldn't find an easy guide to all this anywhere - perhaps not surprising as it's an odd thing to want to do. Jonathan ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: gmirror (was Re: It's time to bite the bullet and do a major upgrade...)
On Wednesday 15 November 2006 10:40, Jonathan McKeown wrote: On Wednesday 15 November 2006 16:58, John Nielsen wrote: It is possible to convert regular devices into gmirror members after they have data on them, but unless you're extremely careful there's a small risk of the gmirror metadata sector overlapping a data sector. OK, I see the warning in the gmirror(8) manpage that gmirror metadata overwrites the last sector of the provider. Is that sector more likely, or less likely, to be in use than any other sector on a non-full disk? If it's equally or less likely the risk is extremely small - which I know is no consolation when it happens! It's generally significantly less likely to even be available for use due to device sizes not dividing evenly into the block sizes used by the filesystem, etc. Depending on what type of device you actually pass to gmirror as a consumer (raw disk, slice, or partition), it should be possible to manually ensure that there are a couple unused sectors at the end. It just depends on how paranoid (or possibly other more reasonable terms) you are. In this case, I'm doing something of a ``stunt upgrade'' anyway: I have two remote boxes to upgrade to 6.1, one of which is running 5.4-RELEASE and one 4.8-RELEASE. Both boxes have 80GB drives, and on my last flying visit I added to each box a blank 80GB drive and a null-modem serial link to a neighbouring ssh-accessible box. The plan is to ssh to the neighbour box, establish a serial console on the upgrade target, install 6.1 from scratch over the network on the blank drive and then make it the only drive in a gmirror. Once that's done, data can be migrated from the original drive, which can then be added to the mirror. I have successfully carried out the procedure on a box in my office (so that I could intervene when it all went horribly wrong, several times) and am in the process of documenting it: as I said earlier, I couldn't find an easy guide to all this anywhere - perhaps not surprising as it's an odd thing to want to do. Jonathan ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: gmirror (was Re: It's time to bite the bullet and do a major upgrade...)
On Wednesday 15 November 2006 18:52, John Nielsen wrote: [risk that last sector of geom(4) provider is already in use] It's generally significantly less likely to even be available for use due to device sizes not dividing evenly into the block sizes used by the filesystem, etc. Depending on what type of device you actually pass to gmirror as a consumer (raw disk, slice, or partition), it should be possible to manually ensure that there are a couple unused sectors at the end. It just depends on how paranoid (or possibly other more reasonable terms) you are. I've always maintained that the correct question to ask a sysadmin is not Are you paranoid? but rather Are you paranoid *enough*? grin / Jonathan ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
