Sébastien Luttringer posted on Thu, 14 Jul 2016 13:18:49 +0200 as excerpted:
> I have a performance issue with «btrfs replace» with raid5 and a _missing_ > device. My btrfs rely on 6x4TB HDD and the operating system is an Archlinux. > > In a nutshell, I will need 23 to 46 days to replace on missing disk. If you're still posting about this, it means you haven't been keeping up with list discussion over the last couple weeks and thus have missed the following. I'll leave it to you to find the threads and get the details if you want, but here's the basics: 1) Btrfs raid56 mode has never really gotten to the stability level of the rest of btrfs, and recently a couple of fundamental defects in the current implementation have come to light, that unfortunately might well require a full rewrite to correct. As such, btrfs raid56 mode, while never recommended except for those willing to be on the bleeding edge, is now negatively recommended, with the recommendation for those already using it being to switch to something more stable at their soonest convenience and to *ensure* that they either have backups or simply don't care about losing the data in the mean time. 2) Replace's often impractically slow performance in raid56 mode with a missing device was one of the known bugs keeping raid56 mode from being considered stable even before the above mentioned fundamental defects had come to light. As such, for raid56 mode with a missing device, btrfs device add of the replacement, followed by btrfs device delete of the missing/failed drive (which forces a rebalance as part of the device delete), seems to be much faster, and is recommended, for raid56 mode with a missing device only, instead of btrfs replace. So there's a workaround for your immediately reported problem, but that doesn't change the fact that there are fundamental issues with the current implementation, and that as such, getting off of raid56 mode as soon as convenient, and ensuring good backups of anything you don't want to lose in the mean time, is now recommended. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
