Messages in this thread | | | From | Duncan <> | Subject | Re: [RFC PATCH v1 0/5] BTRFS hot relocation support | Date | Tue, 21 May 2013 02:22:34 +0000 (UTC) |
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zwu.kernel posted on Mon, 20 May 2013 23:11:22 +0800 as excerpted:
> The patchset is trying to introduce hot relocation support > for BTRFS. In hybrid storage environment, when the data in rotating disk > get hot, it can be relocated to nonrotating disk by BTRFS hot relocation > support automatically; also, if nonrotating disk ratio exceed its upper > threshold, the data which get cold can be looked up and relocated to > rotating disk to make more space in nonrotating disk at first, and then > the data which get hot will be relocated to nonrotating disk > automatically.
One advantage of a filesystem implementation, as opposed to bcache or dmcache, is arguably a corner-case, but it's /my/ corner-case, so...
I run an intr*-less (I guess technically, empty initramfs) monolithic- kernel boot, using the kernel commandline root= and (formerly) md= and related logic to choose/assemble/mount root directly from the kernel command line via bootloader (grub2). Thus, any user-space-required-to- mount-root is out, since I don't have an initr* and thus no early userspace. That means both lvm2 and dmcache (AFAIK) are out. I'm not sure about bcache, but it has other negatives, particularly against btrfs- raid-1 and I'd guess md/raid-1 as well.
Much like md before it, btrfs, while normally requiring the user-space- required device-scan to properly handle multiple devices, has kernel- command-line options that allow direct kernel multi-device assembly without the help of early-userspace/initr*.
So in-btrfs hot-relocation support building on the existing kernel- command-line multi-device assembly options would definitely be welcomed by all us no-initr* folks looking at SSDs but not able to afford them for /everything/ just yet. =:^)
(That said, even if accepted, your solution's a bit late for my own current needs, but there's surely going to be others hitting the same issue in a few kernel cycles when your patches could be mainline btrfs, and having the option at my next upgrade cycle say a couple years out would be very nice, 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
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