Re: LVM creation methods

[Darac Marjal]

On Fri, Jul 20, 2012 at 05:35:03PM +0500, Muhammad Yousuf Khan wrote:
 i was reading a document where a person has configured physical volume
 and didn't use fdisk
   he just directly created the partition by pvcreate /dev/sda
 
 and there are some documents which shows the utilization of fdisk and
 converting sda1 to 8e type  which is LVM.
 
 so the question is what is the difference b/w creating it directly on
 disk by pvcreate command and by using fdisk.

With one, you're using the whole disk, with the other, you're using a
portion of the disk. If you want to use the disk with non-LVM-aware
operating systems, then you'll need to partition the disk and give them
a partition. Bear in mind that non-LVM-aware probably includes your
BIOS, too, so a whole-disk PV is unbootable.

That said, if you only want to use that disk for LVM, then there is no
issue with using the whole disk. In fact, for Advanced Format disks and
SSDs, it may be preferable as you're more likely to get the alignment
right on them.

 
 actually i have just created the partition via direct command
 pvcreate /dev/sda  it is fully functionally and i can use it as a
 partition but when i fdisk -l /dev/sda  it shows that the disk is
 empty. so i am worried that is it the proper way to do it or else i
 may not end up with consequences.

fdisk only reads (as far as I'm aware) PC-style partition tables. If it
says the disk is empty, what it's saying is that there's no partition
table there. If you had a GPT on there, you'd likely get the same
message (actually, newer versions DO detect GPT and print a complaint).

Use the right tools for the job. If you have a partition table, read it
with fdisk. If you have a PV on there, use LVM tools.



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Re: LVM creation methods

[Meike Stone]

2012/7/20 Muhammad Yousuf Khan sir...@gmail.com:
 i was reading a document where a person has configured physical volume
 and didn't use fdisk
   he just directly created the partition by pvcreate /dev/sda

 and there are some documents which shows the utilization of fdisk and
 converting sda1 to 8e type  which is LVM.

 so the question is what is the difference b/w creating it directly on
 disk by pvcreate command and by using fdisk.


from the manual page of pvcreate:

pvcreate initializes PhysicalVolume for later use by the Logical
Volume Manager (LVM). Each PhysicalVolume can be a disk partition,
whole disk, meta device, or loopback file. For DOS disk partitions,
the partition id should be set to 0x8e using fdisk(8), cfdisk(8), or a
equivalent. For whole disk devices only the partition table must be
erased, which will effectively destroy all data on that disk.

So if you use a whole disk, it must be erased and have no partitions ...
Nothing is wrong

Meike


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Re: LVM creation methods

[Muhammad Yousuf Khan]

thanks it is very clear,

yes, i am using the second disk just for storage purpose. so i am not
worried about the booting since it is already been handled via
/dev/sdb
so no issues for me.

Thanks both Meike and Darac

On Fri, Jul 20, 2012 at 5:53 PM, Darac Marjal mailingl...@darac.org.uk wrote:
 On Fri, Jul 20, 2012 at 05:35:03PM +0500, Muhammad Yousuf Khan wrote:
 i was reading a document where a person has configured physical volume
 and didn't use fdisk
   he just directly created the partition by pvcreate /dev/sda

 and there are some documents which shows the utilization of fdisk and
 converting sda1 to 8e type  which is LVM.

 so the question is what is the difference b/w creating it directly on
 disk by pvcreate command and by using fdisk.

 With one, you're using the whole disk, with the other, you're using a
 portion of the disk. If you want to use the disk with non-LVM-aware
 operating systems, then you'll need to partition the disk and give them
 a partition. Bear in mind that non-LVM-aware probably includes your
 BIOS, too, so a whole-disk PV is unbootable.

 That said, if you only want to use that disk for LVM, then there is no
 issue with using the whole disk. In fact, for Advanced Format disks and
 SSDs, it may be preferable as you're more likely to get the alignment
 right on them.


 actually i have just created the partition via direct command
 pvcreate /dev/sda  it is fully functionally and i can use it as a
 partition but when i fdisk -l /dev/sda  it shows that the disk is
 empty. so i am worried that is it the proper way to do it or else i
 may not end up with consequences.

 fdisk only reads (as far as I'm aware) PC-style partition tables. If it
 says the disk is empty, what it's saying is that there's no partition
 table there. If you had a GPT on there, you'd likely get the same
 message (actually, newer versions DO detect GPT and print a complaint).

 Use the right tools for the job. If you have a partition table, read it
 with fdisk. If you have a PV on there, use LVM tools.


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