Booting - Enterprise Volume Management System

[Alexander Skwar]

· Thiers Botelho <thiersb at gmail.com>:

> Thnx Alex, please read below.
> 
> On 8/12/06, Alexander Skwar <listen at alexander.skwar.name> wrote:
>> · Thiers Botelho <thiersb at gmail.com>:
>>
>> > On 8/11/06, Alexander Skwar <listen at alexander.skwar.name> wrote:
>> >>
>> >> Yes, it has. It cannot be used for filesystems on a "dual" boot
>> >> system which should be used for data exchange, as LVM can ONLY
>> >> be used with Linux. No other OS can read Linux LVM.
> 
> Seems that your statement above won't remain true for very long. I
> just found http://www.chrysocome.net/virtualvolumes , which while
> still in beta will soon be able to do "Reads and Writes LVM2" on
> Windoze.

Hey, that's great! Thanks!

>> >> Alexander Skwar
>> >
>> > Based on your statement above, I'd like to know if the following is
>> > feasible (and well, if it makes sense of course):
>> >
>> > - A triple-boot system with WinXP, Ubuntu and, say, Fedora 5 ;
>> >
>> > - One primary partition for windoze C: drive and one extended
>> > partition to accomodate all the rest ;
>> >
>> > - one [or more] VFAT logical partitions for data exchange among the 3
>> > systems (I know, no data security at all here) ;
>>
>> Because of that, I'd recommend ext2. There are drivers for Windows,
>> which allow accessing ext2 from Windows.
> 
> Thnx for the update. I knew previously about
> http://www.chrysocome.net/explore2fs which only _reads_ ext* FSes, but
> its younger brother virtualvolumes will also be able to do "Reads and
> Writes EXT2/EXT3".

Good to know, that there's a ext3 driver for Windows. I didn't know
that.

> However, their FAQ states:
> "Access rights are not maintained. All users can access all the
> directories and files of an Ext2 volume. "
> Therefore I see no real advantage in following your recommendation
> (i.e., ext2 for data exchange instead of vfat). Did I miss something ?

Well - at least on the Linux side, the access permissions are
preserved ;) Granted, you lose this on the Windows side - but
with FAT, you NEVER have access permissions.

OTOH: What about NTFS? With ntfs-3g, you can access NTFS
easily and, so they say, reliably from Linux. This way,
you keep the access perms on the Windows side but lose them
when accessing from Linux ;)

> I suppose that /swap can be under LVM too, right ?

Yep, it can - but if you're going to do suspend-to-disk
with Linux, swap cannot be in LVM. suspend-to-disk uses
a swap partition to store the data.

>> Ie. I'd use the SAME VG with Ubuntu and FC5.
>>
> 
> Makes sense.
> 
>> Hm - actually, I'd make the PV a primary partition, so that
>> Windows has problems accessing the partition.
> 
> Now I'm not thoroughly convinced of this. My understanding is that
> Windows can freely access any number of primary partitions. The access
> restrictions, as I understand them, would come from types of
> filesystems rather than partition types.

What you write makes sense. At least in DOS based Windows (95, 98, ME),
Windows could only access one primary partition. If you needed more
partitions, you HAD to create logical partitions.

In 2000, XP and 2k3, this might be different and might be, as you say.

> One problem I see with making the PV a primary partition would be,
> since all primary partitions come _before_ the logical partitions,

No, they don't. At least not in terms of cylinders:

Disk /dev/hda: 40.0 GB, 40007762432 bytes
255 heads, 63 sectors/track, 4864 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hda1            2001        2062      498015   83  Linux
/dev/hda3               1        2000    16064968+   5  Extended
/dev/hda5               1         123      987934+  83  Linux

Partition table entries are not in disk order


There's no requirement stating how those partitions are ordered. Those
partitions could be accessed with no problems.

> a 
> reduced flexibility in administering filesystem sizes. See, if the PV
> is a _huge_ primary partition, and coming before all the logical
> partitions, the logical partitions for two /boot's plus the ones for
> the data exchange would all have to be squeezed against the end
> boundary of the disk. I surely wouldn't want that - some loss of
> flexibility in administering space and increased seek times for many
> processes.

Hm - increased seek time for accessing the boot partitions?
Well, as there isn't much what's read from /boot, I don't see
that as a real issue ;)

But if you feel more comfortable with creating logical partitions:
Go for it! There's nothing bad with doing so ;)

Alexander Skwar
-- 
Bei vielen Leuten beginnt das Gewissen erst dort, wo der Vorteil
aufhört.
                -- Haile Selassie I.