On Tuesday December 6, djani22@xxxxxxxxxxxxx wrote: > > ----- Original Message ----- > From: "Neil Brown" <neilb@xxxxxxx> > To: "JaniD++" <djani22@xxxxxxxxxxxxx> > Cc: <linux-raid@xxxxxxxxxxxxxxx> > Sent: Tuesday, December 06, 2005 1:32 AM > Subject: Re: RAID5 resync question > > > > On Tuesday December 6, djani22@xxxxxxxxxxxxx wrote: > > > Hello, list, > > > > > > > > > Is there a way to force the raid to skip this type of resync? > > > > Why would you want to? > > The array is 'unclean', presumably due to a system crash. The parity > > isn't certain to be correct so your data isn't safe against a device > > failure. You *want* this resync. > > Thanks for the warning. > Yes, you have right, the system is crashed. > > I know, it is some chance to leave some incorrect parity information on the > array, but may be corrected by next write. Or it may not be corrected by the next write. The parity-update algorithm assumes that the parity is correct. > On my system is very little dirty data, thanks to vm configuration and > *very* often flushes. > The risk is low, but the time what takes the resync is bigger problem. :-( > > If i can, i want to break this resync. > And same on the fresh NEW raid5 array.... > > (One possible way: > in this time rebuild the array with "--force-skip-resync" option or > something similar...) If you have mdadm 2.2. then you can recreate the array with '--assume-clean', and all your data should still be intact. But if you get corruption one day, don't complain about it - it's your choice. > > > > > If you are using 2.6.14 to later you can try turning on the > > write-intent bitmap (mdadm --grow /dev/md0 --bitmap=internal). > > That may impact write performance a bit (reports on how much would be > > appreciated) but will make this resync-after-crash much faster. > > Hmm. > What does this exactly? Divides the array into approximately 200,000 sections (all a power of 2 in size) and keeps track (in a bitmap) of which sections might have inconsistent parity. if you crash, it only syncs sections recorded in the bitmap. > Changes the existing array's structure? In a forwards/backwards compatible way (makes use of some otherwise un-used space). > Need to resync? :-D You really should let your array sync this time. Once it is synced, add the bitmap. Then next time you have a crash, the cost will be much smaller. > Safe with existing data? Yes. > > What do you think about full external "log"? Too much overhead without specialised hardware. > To use some checkpoints in ext file or device to resync an array? > And the better handling of half-synced array? I don't know what these mean. NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
