Kyle Gates posted on Mon, 30 Jan 2012 08:58:41 -0600 as excerpted: > I've been having good luck with my /boot on a separate 1GB RAID1 btrfs > filesystem using grub2 (2 disks only! I wouldn't try it with 3). I > should note, however, that I'm NOT using compression on this volume > because if I remember correctly it may not play well with grub (maybe > that was just lzo though) and I'm also not using subvolumes either for > the same reason.
Thanks! I'm on grub2 as well. It's is still masked on gentoo, but I recently unmasked and upgraded to it, taking advantage of the fact that I have two two-spindle md/raid-1s for /boot and its backup to test and upgrade one of them first, then the other only when I was satisfied with the results on the first set. I'll be using a similar strategy for the btrfs upgrades, only most of my md/raid-1s are 4-spindle, with two sets, working and backup, and I'll upgrade one set first. I'm going to keep /boot a pair of two-spindle raid-1s, but intend to make them btrfs-raid1s instead of md/raid-1s, and will upgrade one two-spindle set at a time. More on the status of grub2 btrfs-compression support based on my research. There is support for btrfs/gzip-compression in at least grub trunk. AFAIK, it's gzip-compression in grub-1.99-release and lzo-compression in trunk only, but I may be misremembering and it's gzip in trunk only and only uncompressed in grub-1.99-release. In any event, since I'm running 128 MB /boot md/raid-1s without compression now, and intend to increase the size to at least a quarter gig to better align the following partitions, /boot is the one set of btrfs partitions I do NOT intend to enable compression on, so that won't be an issue for me here. And since for /boot I'm running a pair of two-spindle raid1s instead of my usual quad-spindle raid1s, you've confirmed that works as well. =:^) As a side note, since I only recently did the grub2 upgrade, I've been enjoying its ability to load and read md/raid and my current reiserfs directly, thus giving me the ability to look up info in at least text- based main system config and notes files directly from grub2, without booting into Linux, if for some reason the above-grub boot is hosed or inconvenient at that moment. I just realized that if I want to maintain that direct-from-grub access, I'll need to ensure that the grub2 I'm running groks the btrfs compression scheme I'm using on any filesystem I want grub2 to be able to read. Hmm... that brings up another question: You mention a 1-gig btrfs-raid1 / boot, but do NOT mention whether you installed it before or after mixed- chunk (data/metadata) support made it into btrfs and became the default for <= 1 gig filesystems. Can you confirm one way or the other whether you're running mixed-chunk on that 1-gig? I'm not sure whether grub2's btrfs module groks mixed- chunk or not, or whether that even matters to it. Also, could you confirm mbr-bios vs gpt-bios vs uefi-gpt partitions? I'm using gpt-bios partitioning here, with the special gpt-bios-reserved partition, so grub2-install can build the modules necessary for /boot access directly into its core-image and install that in the gpt-bios- reserved partition. It occurs to me that either uefi-gpt or gpt-bios with the appropriate reserved partition won't have quite the same issues with grub2 reading a btrfs /boot that either mbr-bios or gpt-bios without a reserved bios partition would. If you're running gpt-bios with a reserved bios partition, that confirms yet another aspect of your setup, compared to mine. If you're running uefi-gpt, not so much as at least in theory, that's best-case. If you're running either mbr-bios or gpt-bios without a reserved bios partition, that's a worst-case, so if it works, then the others should definitely work. Meanwhile, you're right about subvolumes. I'd not try them on a btrfs /boot, either. (I don't really see the use case for it, for a separate /boot, tho there's certainly a case for a /boot subvolume on a btrfs root, for people doing that.) -- 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
