Dirk Lutzebaeck posted on Sun, 22 Jan 2012 16:05:14 +0100 as excerpted: > I have setup a RAID1 using 3 devices (500G each) on separate disks. > After removing one disk physically the filesystem cannot be mounted in > degraded nor in recovery mode.
> - latest kernel 3.2.1 and btrfs-tools on xubuntu 11.10 > What is happening? RAID1 should be mountable degraded with one > missing/removed device. Note that I'm only researching btrfs for my own systems at this point and am not using it yet. However, because I *AM* researching it and already read thru most of the wiki documentation, it's fresh in mind. Here's what the wiki says, tho of course it could be outdated: https://btrfs.wiki.kernel.org/ >From the multiple devices page: >> By default, metadata will be mirrored across two devices and data will >> be striped across all of the devices present. Question: Did you specify -m raid1 -d raid1 when you did the mkfs.btrfs? While the -m raid1 would be the default given multiple devices, the -d raid1 is not. If you didn't specify -d raid1, you'll have raid0/striped data with only the metadata being raid1/mirrored, thus explaining the problem. At least with all devices present, the following should show the raid level actually used (from the use cases page): >> On a 2.6.37 or later kernel, use >> >> btrfs fi df /mountpoint >> >> The required support was broken accidentally in earlier kernels, >> but has now been fixed. Also note since you're running a 3-device btrfs-raid-1, tho it shouldn't affect a single device dropout, from the sysadmin guide page (near the bottom of the raid and data replication section): >> With RAID-1 and RAID-10, only two copies of each byte of data are >> written, regardless of how many block devices are actually in use >> on the filesystem. IOW, unlike standard or kernel/md raid-1, that 3-device btrfs-raid-1 will **NOT** protect you if two of the three devices go bad before you've had a chance to bring in and balance to a replacement for the first bad device. As I said I'm just now researching my own btrfs upgrade, and don't know for sure whether that's true or not, but if it is, it's a HUGE negative for me, as I'm currently running 4-way kernel/md RAID-1 on an aging set of drives, and was hoping to upgrade to btrfs raid-1 for the checksummed integrity. But given the age of the drives I really don't want to drop below dual redundancy (3 copies), and this two-copies-only (single redundancy) raid-1(-ish) no matter the number of devices, is disappointing indeed! -- 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
