also sprach Alexis Rosen <deb...@alexis.users.panix.com> [2009.05.04.1952
+0200]:
> A1 and B1 are mirrored together by md, making "md0" for use as /boot.
> A2 and B2 EACH and SEPARATELY become an LVM2 PV ("PV1" and "PV2").
> PV1 and PV2 EACH and SEPARATELY become an LVM2 LVG ("LVG1" and "LVG2").
> LVG1 and LVG2 are carved up into a bunch of LVs each.
> /root, /usr, /tmp, and /var are each formed by mirroring together 2 LVs, 1
> each from LVG1 and LVG2, becoming "md1" through "md4".So you are running RAID on LVM. This is backwards in my world. I am not sure we should even support that use case, but I'll leave it up to the LVM people to decide about your patch; if they agree, I'll include the mdadm change you propose. Anyway... > /home is formed by striping together 2 LVs, 1 each from LVG1 and > LVG2, to become "md5". [...] > Why am I not simply using md to mirror the whole disk and then > making LVM volumes on top of that? Because I don't want the whole > thing mirrored. /home needs to be striped. Why don't you then put the main system on LVM-over-RAID on partitions 2 and use partitions 3 as a /home strip set? You might argue that you want full flexibility to move space between the different filesystems, but realistically speaking, /, /usr, and /boot are mostly fixed in size. Put those on LVM-over-RAID (or just pure RAID) and then use the rest for stripe sets or whatever else you might need to accomodate /home and /var. > The heart of the problem, I think, is that there's no easy way to > figure out which /dev/mdNs need to be up before which LVs, and > vice-versa. You could have mdN inside an LV inside another mdN > (and so on). Exact analysis, this is in fact the heart of the problem. But as you say yourself, without a dependency graph, we cannot properly cater to the situation. I am not sure whether this complexity would be justified, given that I would never suggest anyone to run RAID off non-physical devices, unless you are doing testing and/or are prepared to deal with the pain. But as I said above, if the LVM folks think your patch is sensible, I won't object. If I feel belligerent, I might throw in a pinch of cryptsetup though. "My LVM on RAID on encrypted LVM doesn't work!" > Do I need to send this patch somewhere else to have it considered? File a bug against LVM and put me on X-Debbugs-Cc. If they fix it, I'll add the prerequisite to mdadm. Thanks, -- .''`. martin f. krafft <madd...@d.o> Related projects: : :' : proud Debian developer http://debiansystem.info `. `'` http://people.debian.org/~madduck http://vcs-pkg.org `- Debian - when you have better things to do than fixing systems "we should have a volleyballocracy. we elect a six-pack of presidents. each one serves until they screw up, at which point they rotate." -- dennis miller
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