Re: mdadm break / restore soft mirror
On Thursday December 13, [EMAIL PROTECTED] wrote: What you could do is set the number of devices in the array to 3 so they it always appears to be degraded, then rotate your backup drives through the array. The number of dirty bits in the bitmap will steadily grow and so resyncs will take longer. Once it crosses some threshold you set the array back to having 2 devices to that it looks non-degraded and clean the bitmap. Then each device will need a full resync after which you will get away with partial resyncs for a while. I don't undertand why clearing the bitmap causes a rebuild of all devices. I think I have a conceptual misunderstanding. Consider a RAID-1 and three physical disks involved, A,B,C 1) A and B are in the RAID, everything is synced 2) Create a bitmap on the array 3) Fail + remove B 4) Hot add C, wait for C to sync 5) Fail + remove C 6) Hot add B, wait for B to resync 7) Goto step 3 I understand that after a while we might want to clean the bitmap and that would trigger a full resync for drives B and C. I don't understand why it would ever cause a resync for drive A. You are exactly correct. That is what I meant, though I probably didn't express it very clearly. After you clean out the bitmap, any devices that are not in the array at that time will need a full resync to come back in to the array. NeilBrown - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: mdadm break / restore soft mirror
So the obvious follow up question is: for this scenario does it make sense to only resync the difference between the two bitmaps? E.g. Drive A will have a current bitmap, B will have a stale bitmap. Presumably one could get away with just resyncing the difference. Or is this too much of special case to consider? Jeff - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: mdadm break / restore soft mirror
On Dec 14, 2007 11:13 AM, Jeff Breidenbach [EMAIL PROTECTED] wrote: So the obvious follow up question is: for this scenario does it make sense to only resync the difference between the two bitmaps? Never mind, I see why this won't work. - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: mdadm break / restore soft mirror
Brett Maton wrote: Hi, Question for you guys. A brief history: RHEL 4 AS I have a partition with way to many small files on (Usually around a couple of million) that needs to be backed up, standard methods mean that a restore is impossibly slow due to the sheer volume of files. Solution, raw backup /restore of the device. However the partition is permanently being accessed. Proposed solution is to use software raid mirror. Before backup starts, break the soft mirror unmount and backup partition restore soft mirror and let it resync / rebuild itself. Would the above intentional break/fix of the mirror cause any problems? Probably. If by accessed you mean read-only, you can do this, but if the data is changing you have a serious problem that the data on the disk and queued in memory may leave that part on the disk as an inconsistent data set. If there is a means of backing up a set of files which are changing other than stopping the updates in a known valid state, it's not something which I've seen really work in all cases. DM has some snapshot capabilities, but in fact they have the same limitation, the data on a partition can be backed up, but unless you can ensure that the data is in a consistent state when it's frozen, your backup will have some small possibility of failure. Database programs have ways to freeze the data to do backups, but if an application doesn't have a means to force the data on the disk valid, it will only be a pretty good backup. I suggest looking at things like rsync, which will not solve the changing data problem, but may do the backup quickly enough to be as useful as what you propose. Of course a full backup is likely to take a long time however you do it. -- Bill Davidsen [EMAIL PROTECTED] Woe unto the statesman who makes war without a reason that will still be valid when the war is over... Otto von Bismark - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: mdadm break / restore soft mirror
On Thursday December 13, [EMAIL PROTECTED] wrote: How do I create the internal bitmap? man mdadm didn't shed any light and my brief excursion into google wasn't much more helpful. mdadm --grow --bitmap=internal /dev/mdX The version I have installed is mdadm-1.12.0-5.i386 from RedHat which would appear to be way out of date! WAY! mdadm 2.0 would be an absolute minimum, and linux 2.6.13 as an absolute minimum, probably something closer to 2.6.20 would be a good idea. NeilBRown - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: mdadm break / restore soft mirror
What you could do is set the number of devices in the array to 3 so they it always appears to be degraded, then rotate your backup drives through the array. The number of dirty bits in the bitmap will steadily grow and so resyncs will take longer. Once it crosses some threshold you set the array back to having 2 devices to that it looks non-degraded and clean the bitmap. Then each device will need a full resync after which you will get away with partial resyncs for a while. I don't undertand why clearing the bitmap causes a rebuild of all devices. I think I have a conceptual misunderstanding. Consider a RAID-1 and three physical disks involved, A,B,C 1) A and B are in the RAID, everything is synced 2) Create a bitmap on the array 3) Fail + remove B 4) Hot add C, wait for C to sync 5) Fail + remove C 6) Hot add B, wait for B to resync 7) Goto step 3 I understand that after a while we might want to clean the bitmap and that would trigger a full resync for drives B and C. I don't understand why it would ever cause a resync for drive A. - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
mdadm break / restore soft mirror
Hi, Question for you guys. A brief history: RHEL 4 AS I have a partition with way to many small files on (Usually around a couple of million) that needs to be backed up, standard methods mean that a restore is impossibly slow due to the sheer volume of files. Solution, raw backup /restore of the device. However the partition is permanently being accessed. Proposed solution is to use software raid mirror. Before backup starts, break the soft mirror unmount and backup partition restore soft mirror and let it resync / rebuild itself. Would the above intentional break/fix of the mirror cause any problems? Regards, Brett Brett Maton Linux Consultant RHCE #805007238628267 --- This email, and the contents contained within, are private and confidential between the sender and the individual(s) to whom it is addressed. The contents do not necessarily represent the views of Simplyhealth Group Limited. In the event of misdirection, the recipient is prohibited from using, copying or disseminating it or any information contained in it. If you have received this email in error please notify Simplyhealth immediately by telephone on 0845 075 2020, or by email to [EMAIL PROTECTED] Simplyhealth Group Limited is registered and incorporated in England and Wales as a company limited by guarantee. Its registered office is at Hambleden House, Waterloo Court, Andover, Hampshire, SP10 1LQ, registered no. 5445654. We may record or monitor telephone calls to help improve our service and protect our members. --- - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: mdadm break / restore soft mirror
Brett Maton wrote: Hi, Question for you guys. A brief history: RHEL 4 AS I have a partition with way to many small files on (Usually around a couple of million) that needs to be backed up, standard methods mean that a restore is impossibly slow due to the sheer volume of files. Solution, raw backup /restore of the device. However the partition is permanently being accessed. Proposed solution is to use software raid mirror. Before backup starts, break the soft mirror unmount and backup partition restore soft mirror and let it resync / rebuild itself. Would the above intentional break/fix of the mirror cause any problems? Is there a reason you can't use rsync to just update changes from the previous backup, once you have your initial one? Regards, Richard - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: mdadm break / restore soft mirror
On Wednesday December 12, [EMAIL PROTECTED] wrote: Hi, Question for you guys. A brief history: RHEL 4 AS I have a partition with way to many small files on (Usually around a couple of million) that needs to be backed up, standard methods mean that a restore is impossibly slow due to the sheer volume of files. Solution, raw backup /restore of the device. However the partition is permanently being accessed. Proposed solution is to use software raid mirror. Before backup starts, break the soft mirror unmount and backup partition restore soft mirror and let it resync / rebuild itself. Would the above intentional break/fix of the mirror cause any problems? No, it should work fine. If you can be certain that the device that you break out of the mirror is never altered, then you could add an internal bitmap while the array is split and the rebuild will go much faster. However even mounting a device readonly will sometimes alter the content (e.g. if ext3 needs to replay the journal) so you need to be very careful. NeilBrown - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: mdadm break / restore soft mirror
Proposed solution is to use software raid mirror. Before backup starts, break the soft mirror unmount and backup partition I use this method for backup once a week. One challenge is drives aren't great at steaming data quickly (for the resync) while also doing a lot of random access. Having a little extra redundancy (think 3 or more drives in the RAID-1) can really help. If you can be certain that the device that you break out of the mirror is never altered, then you could add an internal bitmap while the array is split and the rebuild will go much faster. Is this also a viable speedup for the kep rotating backup drives through the array strategy? If so, how much speedup are we talking about? Assume the array changes by 1% before a backup drive gets rotated in again. Jeff - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: mdadm break / restore soft mirror
Proposed solution is to use software raid mirror. Before backup starts, break the soft mirror unmount and backup partition I use this method for backup once a week. One challenge is drives aren't great at steaming data quickly (for the resync) while also doing a lot of random access. Having a little extra redundancy (think 3 or more drives in the RAID-1) can really help. If you can be certain that the device that you break out of the mirror is never altered, then you could add an internal bitmap while the array is split and the rebuild will go much faster. When the device is split from the mirror it will only be read as a raw device by the backup software (NetBackup) and not actually mounted during the process so it really shouldn't be modified in anyway at all. Also during the backup window files will only be being created on remaining device (reports pdf's) so random access shouldn't be a problem either. How do I create the internal bitmap? man mdadm didn't shed any light and my brief excursion into google wasn't much more helpful. The version I have installed is mdadm-1.12.0-5.i386 from RedHat which would appear to be way out of date! Thanks for you help, Brett --- This email, and the contents contained within, are private and confidential between the sender and the individual(s) to whom it is addressed. The contents do not necessarily represent the views of Simplyhealth Group Limited. In the event of misdirection, the recipient is prohibited from using, copying or disseminating it or any information contained in it. If you have received this email in error please notify Simplyhealth immediately by telephone on 0845 075 2020, or by email to [EMAIL PROTECTED] Simplyhealth Group Limited is registered and incorporated in England and Wales as a company limited by guarantee. Its registered office is at Hambleden House, Waterloo Court, Andover, Hampshire, SP10 1LQ, registered no. 5445654. We may record or monitor telephone calls to help improve our service and protect our members. --- - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
