Sjoerd posted on Fri, 25 Sep 2015 15:40:39 +0200 as excerpted: > Is it better to use raw devices for a RAID setup or make one partition > on the drive and then create your RAID from there? > Right now if have one setup that uses raw, but get messages "unknown > partition table" all the time in my logs. > I am planning to create a RAID 5 setup (seems to be stable these days?), > but wondering to deal with raw drives or partitions (4 at the moment). > In the wiki they're referring to raw devices in the examples, but that > could be outdated? Raw device vs. partition (vs mdraid vs dmraid vs lvm) doesn't matter to btrfs. They're all block devices. That unknown partition table log entry is from elsewhere in the kernel, where it would normally read partition tables if there were any to read. It's simply telling you it couldn't find any, to help with diagnostics in case there's supposed to be one. But if you deliberately used a raw device, there isn't supposed to be a partition table, so no big deal. So just ignore the warning as the diagnostic aid for a case that doesn't apply to you, if you like. Or if you find it irritating enough that isn't possible, then do the big partition thing and disappear the warning. No big deal either way. =:^) Tho if the device is either going to be bootable, or you might want to repurpose it to bootable in the future, you may well want to partition it, preferably gpt, and create a couple small partitions to make that easier, before creating the big one. Here, I create both a tiny BIOS-reserved partition, for legacy BIOS boot (which I use now, grub2 installs to it for BIOS systems), and a slightly larger but still tiny EFI-reserved partition, for forward compatibility. The two together still take only an eighth of a gig (128 MiB), which I figure is a fair trade for the additional flexibility it gives me. Here's my layout, FWIW. (This is on SSD where partition order doesn't matter. Since the first sections of a spinning rust device are the fastest, and these will only ever be used for boot if used at all, you might wish to put these last, on that.) Generally 2 MiB minimum alignment, for better efficiency on modern devices, and the first few KiB of a device are taken by the boot sector and partition table. But the BIOS partition is so small and accessed using primitive and inefficient BIOS routines anyway... # Start (MiB) End (MiB) Size (MiB) Name/Description x 0 1 1 GPT/free 1 1 4 3 BIOS/reserved 2 4 128 124 EFI/reserved As you will note, that ends at an even 128 MiB alignment, 1/8 GiB. FWIW, I put another couple small partitions (boot and log) under a gig, ending with GiB alignment, with everything else GiB aligned. And 1/8 GiB is small enough, I'll often start off with that even on USB flash drives. To me it's worth it, just to have the flexibility of making it bootable, should I decide to, without having to move partitions around to fit in the boot stuff. Then I partition up the rest, or leave it one big partition, as the use-case calls for. As an additional benefit, because I use this layout consistently, should I need to (tho with gpt having checksumming and a partition table at each end of the device, the chance of entirely losing it without the whole device being junk is dramatically lowered), I can recreate it with good confidence, knowing the normal partitions always start at 128 MiB. -- 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 majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
