Distriputed LVM and striped LVM

[senthil_kumar_1]

Hi All,

1)How to create distriputed LVM and striped LVM?

2)What is the purpose of those LVM?

3)What is the default one?

[James R. Ferguson]

Hi Senthil:

1. The choices are made during your logical volume creation. See the manpages for 'lvcreate'.

2. The purpose is to spread I/O across as many physical disk as possible to reduce disk queue lengths on any one device and load-level I/O. You might think of distributed extents as very large stripes. Two drawbacks to using either is if you need to grow your logical volume you must add physical volumes to its volume group in n-units where 'n' equals the number of physical volumes over which extents are spread. In my opinion, with modern SAN farms with large amounts of cache and techniques (under-the-covers) to spread data and/or dynamically move it around to eliminate hot-spots, striping and distributed extents are less useful than they once were.

3. The default is neither. Once again, look at the 'lvcreate' manpages.

Regards!

...JRF...

[Johnson Punniyalingam]

1)How to create distriputed LVM and striped LVM?

http://www.scribd.com/doc/7782998/HPUX-System-Administrators-Guide-Logical-Volume-Management

2)What is the purpose of those LVM?

http://tldp.org/HOWTO/LVM-HOWTO/whatisvolman.html

3)What is the default one?

its depends, how you want, by default "normal" logical volume - may (1 mirror copies)
man lvcreate -> more information

[R.K. # · Accepted solution]

Hi Senthil,

1)How to create distributed LVM and striped LVM?
See Attachment

2)What is the purpose of those LVM?
See Attachment (Advantages & Disadvantages gives you the purpose)

3)What is the default one?
While creating LV you need to specify which type you are going for, else it will neither be distributed nor striped.

[Kranti Mahmud]

Si Senthil,

Check the below links:

http://networktechnologist.com/tips-hpux-lvm.html

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01919369/c01919369.pdf (BSC link updated by admin)

Rgds-Kranti

[sujit kumar singh]

Prior to 11.31 Releases of HP-UX the Distributed Extent BAsed Striping is the implementation of RAID10 on HP_UX LVM.
You can keno more if you can refer to the man pages of lvcreate/lvextend.
this is achieved using the /etc/lvmpvg the most.
lvcreate -D y -s g : -D for Distributed and -s for Striped.

The distributed allocation policy
REQUIRES the PVG-strict allocation
policy (-s g) to ensure that mirrors of
distributed extents do not overlap (for
maximum availability).

lvcreate(1M) will obtain the list of
available physical volumes from
/etc/lvmpvg. See vgextend(1M) for more
information on physical volume groups
and /etc/lvmpvg.

When a logical volume with distributed
extents is mirrored, the resulting
layout is commonly referred to as
EXTENT-BASED MIRRORED STRIPES.

Note that EXTENT-BASED MIRRORED STRIPES
can be created without the distributed
allocation policy by adding one extent
at a time to the desired physical
volumes through lvextend(1M).

The distributed allocation policy is
incompatible with the striped scheduling
policy (-i stripes) and the contiguous
allocation policy (-C y).

The lvchange(1M) command can be used to
assign the distributed allocation policy
to an existing logical volume.

Hewlett-Packard Company - 4 - HP-UX 11i Version 2: Jul 2007


Striped LVM is the one in which the data is Striped across differnet Columns also called Diffrerent PVs.
lvcreate -I -i 3 etc :

I Stripe Unit Size and i for number of Columns.

Default is none: depends on what you choose your LV to be like.

[mvpel]

Don't forget that block-striped volumes (as opposed to extent-striped volumes) can't be mirrored by MirrorDisk/UX.

[sujit kumar singh]

Hi Mvpel,

Though this is an information and i have never done/come across this but .. seems that
that limitation is overcome perhaps in 11.31 Sep 2008 Release where a simple striped volume can also be mirrored.

this can be reffered to page 12 of this documrnt.

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01919369/c01919369.pdf (BSC link updated by admin)

regards
sujit