The automatic partitioning scheme used in FC4 is very inflexible, since it creates a single logical volume occupying virtually the whole available disk space. This partition scheme cannot then be changed without either a considerable amount of expertise (and risk), or else dumping the whole system and re- installing. To be honest, I think the default is plain wrong and should be changed - in general, defaults should be safe, and should allow newbies to logical volumes (as I was) to set up a system that can later be tailored as they gain experience. But so long as it remains as it is, it needs to be documented in the installation guides (and preferably, in the installation macros themselves). In particular, it would be highly desirable for the documentation to include a warning along the lines of: "Warning: if you use the automatic partitioning scheme, it will be extremely difficult at a later stage to tailor it. If you think you might later need to restructure the partitioning, you should read the documentation on logical volumes, noting that they are easy to extend but very difficult to shrink. You may wish to consider creating a partitioning scheme with relatively small logical volumes, for later extension."
The automatic partitioning scheme uses LVM by default which is far more flexible allows restructuring better than static partitions. Fedora also includes a graphical LVM utility - system-config-lvm which allows you to view and manipulate volumes easily. The installer also provides you a option to review and change the options if required apart from custom partitioning schemes. This is planned to be enhanced even more with a seperate /home volume https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=150670 If you want to learn about LVM, refer to these documents http://www.redhat.com/magazine/009jul05/features/lvm2/ http://www.tldp.org/HOWTO/LVM-HOWTO/ If you want to suggest any further enhancements or bug reports, file it against lvm or anaconda components as appropriate.
Thank you for your comments. While it is true that LVM is far more flexible than static partitions, they are not perfect. In particular, they are extremely difficult to shrink. But this is precisely the requirement that the default partitioning scheme imposes - having used the whole disk space for a single logical volume, the only way a user can later make changes is to shrink that volume (or add more disks). This won't be alleviated much by the proposal under 150670, since the proposal is still to occupy the whole disk, the debate is only about how to split the space.
I should add that the two documents referred to by Sundaram have limited relevance; the first describes how to extend LVM partitions, but not how to shrink them, the point at issue here. The second deals with LVM 1 only; the methods described there do not work with LVM 2.
The installer used static partitions that made use of the whole disk before and it was difficult to either extend OR shrink them. Now if its possible to shrink them, its a improvement over the previous scheme and hence requires no special warning. The fact that the automatic installation uses LVM is already documented in the installation guide, the implication of which is available in several documents, some of which I have referred above. It might useful to add a note that LVM does not allow shrinking if thats the case already and when the next release of Fedora is made. It would be better to file a enhancement suggesting the shrinking be supported against LVM if its not already possible or requested. You might also want to suggest any other enhancements to the default partitioning scheme against Anaconda and drop in the bugzilla numbers here as comments. That would be helpful to keep track of these issues and document them as appropriate. Documenting work arounds is only needed if the tools dont do the right thing and there isnt a way to fix them within constraints. Note: LVM HOWTO also covers LVM2
Can we get some developer confirmation about LVM and shrinking volumes? If necessary, we can document recommendations and workarounds. Bob - do you have a bugzilla report, mailing list thread, or similar to reference? We need some feedback from the LVM developers, and probably the Anaconda developers. If you haven't found any relevant existing bugs, can you file two separate RFEs against Anaconda and LVM? (To 'request' a feature, choose Enhancement under Severity.) I'm reassigning this to the Fedora Installation Guide bugzilla component for consideration, and making it block the FC5 relnotes tracker so we can review if anything more needs to be in the release notes.
Dear Karsten, Thank you for your response, and your guidance on how to handle things, I'm not entirely clear on how bugzilla is supposed to be used. I did submit a bug at (anaconda) https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=170482 but it has been marked as a duplicate of https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=150670 In fact, I think it's a separate, though related, issue - even if the user and system directories are split into separate volumes, the filesystem is still inflexible if the whole available disk space is used. I've now posted it as an rfe also under lvm, as you suggest: https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=170956 There is a fair bit out there on the web on this issue, the most useful thread I found was http://www.linuxquestions.org/questions/showthread.php?s=&threadid=337823&highlight=resize +lvm However I couldn't make this solution work because it seemed that the FC4 boot disk uses /dev/VolGroup00/LogVol00/sbin as its source for lvm binaries, so umounting it (which is necessary for the resize) removes access to the very binaries needed. I posted a query about this at http://www.fedoraforum.org/forum/showthread.php?t=81095 One response suggested I should be able to make the FC4 boot disk work, but again I couldn't get it to work the way suggested. Fortunately, that thread also suggested trying Knoppix. I did that, used info from http://www.knoppix.net/wiki/LVM2 to update lvm on the fly (probably there is a way to do that also for the FC4 boot disk, but I couldn't find it), and finally managed to get the resize done. I posted a thread on how to do it at http://www.fedoraforum.org/forum/showthread.php?t=81353 The bottom line, though, is that LVM completely changes things. The LVM manager is a _really_ nice tool for expanding volumes - it seems to be bullet- and newbie-proof (I didn't see any reports on any problems with it, despite a fair amount of googling). So giving users a default of fairly small sizes, and leaving unallocated space, is no longer a problem - so long as they get a warning that that is what is happening, and what to do about it if they start to bump against the limits. On the other hand, shrinking LVMs is not only difficult - see above - but also inherently dangerous. There are any number of ways in which you could destroy the filesystem in trying to do it. If this can't be changed, then the issues with the defaults need to be documented (of course, if LVM manager were to include a gui for shrinking volumes, that would change things completely - the current defaults would be fine - but I haven't seen any hints that that is in the wind).
Unblocking FC5 release notes; this is a situation best handled in the Installation Guide.
I've now added text to the Installation Guide to advise on leaving unallocated space, and growing LVM volumes to use free space as required, in preference to fully allocating storage and then shrinking volumes to make the space available for reallocation. The "Other Technical Documentation" Appendix now has a link to the LVM HOWTO.
The situation has changed somewhat, since the LVM GUI in FC5 now provides the option (presumably safety-checked) of shrinking volumes. However it's only a partial solution, since it requires unmounting the target volume. So the user must still understand the need to boot from a separate system from the one being updated. Thus it's still a trap for newbies, though not nearly as badly as previously.
Bob: would you mind reviewing the relevant section of the Installation Guide for us? http://fedora.redhat.com/docs/fedora-install-guide-en/fc5/sn-disk-druid.html I don't personally work with LVM much, so you may be able to suggest improvements to the text there.
Created attachment 128412 [details] Suggested revision for Ch 5.1 Dear Stuart, Firstly, thank you for the opportunity to comment. Actually, I think 5.2 is fine, it covers the important issues. The problem is that the users it needs to catch - new users who just want to do everything the 'simple' way, but might later need to change things - aren't going to read 5.2, because as far as they're concerned, 5.1 has effectively told them it's OK to accept the default scheme, so they can ignore 5.2. I've taken the liberty of drafting some minor changes to 5.1 (using nvu - I'm sorry, I'm not sure what tool is normally used for fedora docs). These consist of a warning early on, an extra section 5.1.4 for new users, and some slight changes to the wording in 5.1.3, to be clearer about logical volumes. I hope they can be of use. But I'm also not expert in LVM, so it would be great if they could be checked by one of the LVM gurus.
Thanks - that was very helpful. I've amended 5.1.3, and added information from your 5.1.4 into some existing sections. We tend to encourage users to stick to the defaults unless they have specific reasons (and the understanding) to change them, so I wouldn't feel comfortable suggesting that new users go into manual LVM configuration for their first installations. Hopefully future releases of Fedora will create a separate /home partition by default, as is being discussed on #150670.