LVM questions

[gimp2x]

i have a 120GB drive (ide)
i have a 40GB drive (ide)

the 120GB is partitioned as follows

Disk /dev/hda: 255 heads, 63 sectors, 14589 cylinders
Units = cylinders of 16065 * 512 bytes

Device Boot Start End Blocks Id System
/dev/hda1 1 4 32098+ de Dell Utility
/dev/hda2 * 5 12761 102470602+ 7 HPFS/NTFS
/dev/hda3 12762 12767 48195 83 Linux
/dev/hda4 12768 14589 14635215 f Win95 Ext'd (LBA)
/dev/hda5 12768 14335 12594928+ 83 Linux
/dev/hda6 14336 14589 2040223+ 82 Linux swap

the other is blank/free

how can I convert my system to LVM without having to start off fresh again?

can i somehow make a vg on my 40gb drive and then drag all the contents from the regular drive over to the vg, boot
from it, erase all the crap on the extra partions on the 120GB drive, merge the free space into the rootvg and then
have a partially LVM 120GB drive and a full LVM 40GB drive

err, and also i need an ext2 boot partition, someone wanna coach me through this?


also, the purpose of this is to stripe between the two drives...so i also probably need to figure out how to do that too

[gimp2x]

nobody? can someone move this to the appropriate thread?

[mglauche]

you can do it with lvm.

Once you've created a physical volume with a vg on it, you can move this physiacal volume around, resize it, etc.

example:
2 hardrives, with one big vg, buy a new harddrive, "move" vg away from one of the old harddrives, then expand it to the size of the new harddrive. (hope this is what you mean)

[chavez]

Take a look at EVMS, http://evms.sf.net. The gentoo kernel has support for evms and you can emerge evms to get the evms user space utilties. The user space comes with a GTK gui that can help make some of the LVM configuring easier.

That is, you would create a Linux LVM container (EVMS speak for a VG) using whatever segments (EVMS speak for partitions) or disk you want then create regions (EVMS speak for an LV) from the container.

Make the the LV into volumes so you end up with /dev/evms/lvm/vg/lv nodes. Copy the data over. Later after wiping out your original disk. You can use the "Expand Container" command in EVMS to allow the VG to consume the disk. Then you can expand your volumes if you want or as you need to consume more space. The real nice feature is that if there is an FSIM (File System Interface Modules) available for your filesystem (EVMS 1.1 supports ext2/ext3/, fat16, reseirfs and jfs) then expansion of the volume storage and the expansion of the filesystem will be coordinated by EVMS.

Visit the #evms IRC channel on openprojects.net if you have any questions.
_________________
regards,

Luciano Chavez

[gimp2x]

thanks for all the help, i'll look into this

[BigRedDog]

I've been messing with EVMS. It looks good so far. I have no idea how it compares (performance-wise) to LVM, but it has some nice features. I like how the kernel recognizes the volumes at startup without having to run some userspace utility like vgscan. That should make it really easy to put my root filesystem under EVMS.

However, LVM does have much better documentation. The only way I learned EVMS was by messing around with it, which isn't really an option when you're dealing with important data.

Is there a way to use EVMS during the initial stages of the Gentoo install? Or do I have to install to another partition and copy everything over?

[chavez]

BigRedDog,

Hopefully I can respond to your three questions. If have you have
further questions pleast post them on the evms-devel mailing (the three you asked are all good):

We realized a while back that our docs needed improvement. Our
documenation person is working on a new user's guide that offers a more task oriented approach, i.e. I want to build a software RAID 5 object for use by LVM on top...how do I do that?, as well as recommendations on what you want to start. In other words, I need fault tolerance but not necessarily performance, in this case RAID 1 (mirroring) may be was is recommended and so on.

As for performance comparison, there have been a couple of performance benchmarks comparisons between LVM and EVMS posted on the web. Unfortunetly, I can't find them all at the moment. Watch http://lse.sf.net/benchmarks/evms for new comparison reports.

Lastly, funny you ask about Gentoo installation. The command line
utility could be used assuming you have the user space engine and
necessary engine plugins installed (as well as the EVMS kernel side
built). At the moment, we are working with one of the Gentoo developers on creating Python language bindings around the EVMS application API in order for it to be used by their future installer. Neat, huh?

We're pleased that you've taken the time to try and like EVMS.
_________________
regards,

Luciano Chavez

[arkane]

[chavez]

[arkane]

Wow... yet another world of technology to explore...
*sigh*

For this particular instance, I think just LVM would be the answer. After looking at EVMS, it's a great tool for systems requiring it. However, it might be a "golden hammer" so to speak for someone just looking for LVM's capabilities.

Am I right, or missing the point? (considering LVM is in the kernel, no need to patch, is fairly simple to install... etc)

[BigRedDog]

[quote="arkane"For this particular instance, I think just LVM would be the answer. After looking at EVMS, it's a great tool for systems requiring it. However, it might be a "golden hammer" so to speak for someone just looking for LVM's capabilities.
[/quote]

I was kind of wondering that myself. EVMS seems to have a lot of capability, but I just want something so that I don't have to worry about getting my partition sizes right. My plan was to start off using 1/4 my drive and add more as needed. Using EVMS, the only way I could figure out how to do this was by using a "Linux LVM" container. It makes me wonder if I'm adding unnecessary complexity.

Either way, you're probably going to have to upgrade. According to the EVMS web site, LVM is going to be dropped from the kernel. So it looks like the choice is going to be between EVMS and LVM2.

[chidrob]

I vote for LVM with Gentoo. This is my "mount":

> /dev/hdc6 on / type ext2 (rw,noatime)
> proc on /proc type proc (rw)
> none on /dev type devfs (rw)
> tmpfs on /mnt/.init.d type tmpfs (rw,mode=0644,size=1024k)
> /dev/vg_base/home on /home type ext3 (rw)
> /dev/vg_base/var on /var type ext3 (rw,noatime)
> /dev/vg_base/tmp on /tmp type ext3 (rw,noatime)
> /dev/vg_base/vartmp on /var/tmp type ext3 (rw,noatime)
> /dev/vg_base/usr on /usr type ext3 (rw,noatime)
> /dev/vg_base/portage on /usr/portage type ext3 (rw,noatime)
> /dev/vg_base/distfil on /usr/distfiles type ext3 (rw,noatime)
> /dev/vg_base/opt on /opt type ext3 (rw,noatime)
> /dev/vg_prod/pub on /pub type ext3 (rw,noatime,data=writeback)
> /dev/vg_prod/cvs on /pub/cvs_mirror type ext3 (rw,noatime,data=writeback)
> /dev/vg_prod/cvsup on /pub/cvsup_mirror type ext3 (rw,noatime,data=writeback)
> /dev/vg_prod/ftp on /pub/ftp_mirror type ext3 (rw,noatime,data=writeback)
> /dev/vg_prod/isoimag on /pub/iso_images type ext3 (rw,noatime,data=writeback)
> /dev/vg_prod/hercule on /pub/hercules type ext3 (rw,noatime,data=writeback)
> /dev/vg_prod/ware on /pub/ware type ext3 (rw,noatime,data=writeback)
> /dev/vg_prod/pendent on /pub/pendent type ext3 (rw,noatime,data=writeback)
> /dev/vg_test/qhercul on /zfast/hercules type ext3 (rw,noatime,data=writeback)
> /dev/vg_test/qware on /zfast/vmware type ext3 (rw,noatime,data=writeback)
> bash-2.05a$

vg_prod, vg_test and vg_base are LVM volumes.

I'm using LVM with gentoo for four months now, without problems (but this is a workstation, not a server). In fact, I'm doing stripping, for better perfomance with hercules, althougth without any success.

Thanks to LVM, my Gentoo system is going well after all these months, including the upgrade from two to four hard disks practically "online". I have resize some partitions, etc, also.

In fact, I upgraded to 2.4.19 (vanilla-sources) yesterday without any problem. And I have some appls with "special" modules: dri, vmware, alsa and LVM, of course. You can see that /usr/src is on a LVM partition.

[ghost_o]

[chavez]

[sanity]

EVMS looks very cool. Couple things, though:

It has a lot of new terminology. I have a spare hard drive to play around with, and the ncurses interface makes it easy to do that. Still, it's a lot to learn, and so far all I'm using it for is LVM. Of course, there's always room to grow...

GPT support in EVMS is one thing. GPT support in the boot loader is quite another. I've looked (but haven't found) a patched LILO, and I'd rather use GRUB anyhow, but it only sees the protective MBR. I've tried adding a partition to the protective MBR, and in fact I've even tried messing with the -t flag of fdisk (which doesn't understand gpt) to turn on and off the use of GPT on the drive. It fails, because at any change in the GPT partition table, the protective MBR is overwritten. The only other solution I can think of is kernel-on-a-floppy -- not fun.

It does seem to have unneeded complexity. Does LVM really need to be on a partition? Of course it does, if I intend to have a separate /boot partition. But still, there do seem to be too many layers there -- or at least to many neccessary layers. Am I wrong, or missing something?

And finally, from the looks of resize_reiserfs, I have to shrink partitions offline. This shouldn't matter too much (at least for my system), and I know it's up to Reiser, not EVMS, to implement it. It would be nice, though, and the reiser source is available. Maybe create a big enough file, in the right spot?

Also, a question:

From what LVM looks like, everything is "logical". This must mean there's a possibility for defragmentation. Is there an LVM defragmenter? If so, it should be accessable from EVMS.
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[arkane]

[sanity]

By "defragmentation" I meant the partitions themselves. How does LVM manage when you change the size of the partitions? I thought that was the whole point of LVM -- they are "logical volumes" so you don't need to know or care where they are on disk. But what happens if you've got a 20 gig hd, and you've got a 2 gig partition, a 3 gig partition, and a 5 gig partition, created in that order, and you delete the 3 gig and make a 17 gig?

Seems to me that either you'd have to wait for LVM to move at least 2 gigs of data around, or you'd have to have one of those partitions "fragmented" into two parts. Now, this probably won't be a performance hit for most people under most conditions, but eventually (it always happens) the system will break down. It would be nice if, whenever I had my system down, I could have LVM automatically re-sort those partitions, even separate them for speed by amount used (for example, putting var and swap on faster-spinning areas of the disk). It also doesn't seem like it would be too hard to implement, even online -- Reiser seems to be attempting that one, defragmenting partitions when there's little or no disk i/o.

Of course, I could be wrong, but it does look something like software RAID. Software RAID is fast in theory and in benchmarks, but in practice it does use the CPU and therefore slows the system down. I'm hoping that LVM/EVMS doesn't put too much between the FS and the disk.
_________________
Every time you read a signature, God kills a kitten.

[arkane]