LVM and Thin Provisioning

[Nicolas Michel]

Hello,

I didn't know that thin provinsioning was a feature of LVM! Good to know it
:)
Said that, isn't the future will BTRFS? No need of LVM anymore then since
all of the features will be "packages" in the filesystem.

Nicolas


2012/8/23 John Moser <john.r.moser at gmail.com>

> Gents,
>
> Do you think in the future Ubuntu would benefit from an LVM with thin
> provisioning default whole-disk layout?  At the moment thin
> provisioning is not considered stable, and so it would be
> inappropriate.
>
> I believe that once LVM thin provisioning is stable, it would be
> worthwhile for Ubuntu to use it by default when installing across a
> whole disk.  Essentially with a single large disk, Ubuntu could create
> one big logical volume such that 100% of the disk is /, 100% is /home,
> and some small amount is swap.  This would allow for snapshot backups,
> encryption, and such through the supported LVM interfaces.  More
> importantly, it would allow for the isolation of file systems
> (particularly / and /home) without complex considerations like "how
> big do we make them?"
>
> The down side to this is LVM complexity--power users can't simply pull
> up gparted and manipulate LVM partitions, slide things around to
> install an alternate OS, etc, without learning some new tools.  I
> think power users would plan ahead for that, and other users who do a
> full disk install won't particularly have such needs because they'll
> be of the "Install one Linux because I want my computer to work"
> variety.
>
> Users who are resizing an existing OS and using part of the disk may
> legitimately have a middle ground where they eventually move to resize
> partitions (remove the old OS or Ubuntu) and find that their basic
> knowledge is suddenly useless and they don't know where to go from
> here or really want to put in that kind of effort.  From that
> perspective, shrinking a Windows partition and putting an LVM Physical
> Volume next to it with a complex Logical Volume layout may not be a
> great idea; the distinction between "power user" and "regular user"
> does have a gray-zone border, and these sorts of installs fall within
> it much more often than straight-up whole disk installs.  But then,
> maybe it'd be perfectly fine anyway.
>
> LVM thin provision does legitimize automatic file system migration.
> Passing TRIM through a thin provisioned LVM volume doesn't just knock
> a block off an SSD; it tells the thin provisioning layer that that
> block is free.  When an entire extent is TRIMed off, it becomes
> available again (as is my understanding, anyway).  So a user on Ubuntu
> with ext3 migrating to ext4 loses out on a lot of features that ext4
> simply has to be created from scratch for; well you can create a new
> thin root, move the data across (TRIMing as you go), and then remove
> the old LV.  Even if the disk is 90% full.  Same for when some fool
> has experimented with btrfs and realizes there's no fsck tool (fsck
> doesn't FIX btrfs, it just tells you if it's broken) and he wants to
> go back to ext4 or XFS.
>
> Thoughts?
>
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-- 
Nicolas MICHEL
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