Recently Dean Gaudet, in thread titled 'Feature Request/Suggestion - "Drive Linking"', mentioned his document, http://arctic.org/~dean/proactive-raid5-disk-replacement.txt I've read it, and have some umm.. concerns. Here's why: .... > mdadm -Gb internal --bitmap-chunk=1024 /dev/md4 > mdadm /dev/md4 -r /dev/sdh1 > mdadm /dev/md4 -f /dev/sde1 -r /dev/sde1 > mdadm --build /dev/md5 -ayes --level=1 --raid-devices=2 /dev/sde1 missing > mdadm /dev/md4 --re-add /dev/md5 > mdadm /dev/md5 -a /dev/sdh1 > > ... wait a few hours for md5 resync... And here's the problem. While new disk, sdh1, are resynced from old, probably failing disk sde1, chances are high that there will be an unreadable block on sde1. And this means the whole thing will not work -- md5 initially contained one working drive (sde1) and one spare (sdh1) which is being converted (resynced) to working disk. But after read error on sde1, md5 will contain one failed drive and one spare -- for raid1 it's fatal combination. While at the same time, it's perfectly easy to reconstruct this failing block from other component devices of md4. That to say: this way of replacing disk in a software raid array isn't much better than just removing old drive and adding new one. And if the drive you're replacing is failing (according to SMART for example), this method is more likely to fail. /mjt - 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
