Date: Thu, 03 Oct 1996 10:43:41 +0200 From: Jim Reid <jim.reid@eurocontrol.be> To: "Kevin P. Neal" <kpneal@pobox.com> Cc: Terry Lambert <terry@lambert.org>, avalon@coombs.anu.edu.au (Darren Reed), jrg@demon.net, mrg@eterna.com.au, hackers@freebsd.org, tech-kern@netbsd.org Subject: Re: VPS mailing list, BSD interest? Message-ID: <9968.844332221@heron.pst.cfmu.eurocontrol.be> In-Reply-To: Your message of "Thu, 03 Oct 1996 01:08:55 EDT." <1.5.4.32.19961003050855.006b6f70@mindspring.com>
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>>>>> "Kevin" == "Kevin P Neal" <kpneal@pobox.com> writes: Kevin> It would actually break FFS for a partition to grow Kevin> underneath it? Not necessarily. For those who are unfortunate to have LVM, there is a utility called extendfs which allows you to expand the filesystem - here it's just ufs, but I suppose would work for vxfs too - into new logical volumes. Kevin> Would newfs_ffs (or whatever) know which devices could Kevin> support the filesystem? How would that work? I guess it works by having some kernel struct which has a number of block counts and disk devices and offsets which comprise each logical volume. Kevin> Lemmie see if I have this straight: 1) User program decides Kevin> to grow/shrink a partition. 2) User program tells Kevin> partition to grow/shrink 3) Virtual partition asks for the Kevin> permission of the filesystem 4) Assuming they agree, they Kevin> work together somehow to do whatever -- Filesystem must Kevin> make sure there is enough space available to shrink down Kevin> into. Non-resizable filesystems would just veto the whole Kevin> shebang. Not exactly. In the LVM paradigm, physical volumes - disks or bits of disks can be added and removed from a logical volume more or less at will. [Obviously there are sanity checks that the PV isn't used.] Once you've added a new PV to the logical volume, extendfs is used to diddle the superblocks so the filesystem can use the new space. Kevin> Ok. Doesn't this assume that whatever is sitting on top of Kevin> the partition is a filesystem? What if it isn't? What if a Kevin> database or something or other is sitting on top? Would Kevin> resizing be possible? Wouldn't the mechanism of Kevin> communicating the resize be different because of the user Kevin> program hitting the disk instead of going through a Kevin> filesystem? It depends on what it's being used for. Kevin> Third case: What do you do about resizing a swap partition? This is hardly different from adding an extra swap device. Just add a vnode which points at the extra space and use swapon to make the kernel use it.
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