Fedora 15, new and exciting plans

Milan Broz mbroz at redhat.com
Mon Nov 15 12:02:41 UTC 2010

On 11/14/2010 12:41 AM, Richard W.M. Jones wrote:

>> 1. http://fedoraproject.org/wiki/Features/NoDefaultLVM

Info on this page is completely obsolete!

> | * Certain filesystem features (ext3 barriers) are unavailable when run
> |   on top of LVM.

No longer true, barriers (resp. flush) are fully supported with LVM now.

> | * Software RAID performance is greatly reduced when layered on LVM.

Not true. The main performance problem was that sometimes LVM over RAID
created misaligned devices with huge performance loss.

Because both MD/DM subsystems now respects topology info and also use default
1MB alignment if there is not topology info, this is fixed.
Applies to LUKS too for FDE (full disk encryption).

Btw LVM over MD RAID is very common configuration.

Moreover LVM will not duplicate RAID functionality in kernel but will try
to use existing MD code (see dm-devel list track patches and for more info).

> | * LVM partitions are not automatically assembled by the desktop systems.

No idea where this come from? All required volumes are assembled.
Moreover, this is not lvm problem but problem in desktop extensions like udisks.

(Also image you attach iSCSI device with LVM  with hundreds of LVs.
You probably do not want to activate everything automatically - this
is job for admin to setup such configurations.
Counterexample is USB disk - most of users want to activate it automatically.)

Also note:
- Discard/TRIM is supported for linear mappings and multipath in LVM in 2.6.37.

I am not sure if LVM default is good or not for Fedora but please do not use
obsolete arguments here - almost everything you are complaining about
was fixed or there are known ways how to improve or fix  it
(like move scanning of devices in lvm to udev responsibility etc.)

You can replace some functionality with btrfs, but lvm+luks+raid+artbitrary fs
is still very flexible - maybe not for you but definitely for some users.


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