Messages in this thread | | | Date | Wed, 4 Nov 1998 00:55:53 -0500 (EST) | From | "Albert D. Cahalan" <> | Subject | Re: Volume Managers in Linux |
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James Fidell writes: > Quoting Theodore Y. Ts'o (tytso@MIT.EDU):
>> I've never claimed that the ext2 is the best way to do RAID; I think MD >> is the way to do that. However, allowing ext2 to be able to support >> filesystems which span multiple block devices is a good thing to do, and >> a cleaner way of supporting multivolume support. Examples of >> filesystems which do this include the UDF filesystem used by DVD-ROM's, >> and Digital Unix's Advanced Filesystem. > > What "feels wrong" about this to me is that all fs implementations are > then required to implement multiple device spanning, or they can't be > used on spanning partitions at all.
You always get simple concatenated partition support from MD. Filesystem support is only needed if you want to go beyond that.
> Conceptually it seems simpler to have the virtual layer which understands > how to span multiple partitions, but which looks like a block device from > the "user" view, thus allowing any filesystem type to be used upon it, be > that ext2, reiserfs, ufs or something even better that we haven't even
For UFS, you'd want to be disk-level compatible with whatever Solaris and FreeBSD have. Hans Reiser wants to span Reiserfs across a network, but that won't work too well with a dumb LVM system. NTFS has it's own system of course, and couldn't use a Linux-specific LVM. That leaves only ext2 and a collection of odd filesystems. Since ext2 would have to be aware of the system anyway, the extra layer can be eliminated.
It has taken a long time to generate enough desire to advance the way Linux deals with partitions. The LVM is a small step that will drain away some of the desire to help code a device-spanning filesystem. Minor issues of performance and awkwardness might not be enough to get people hacking on something better for several years. I can see several years of "just unmount, resize the LVM, resize ext2, and mount the filesystem again". That's offline, not online.
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