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Re: [linux-lvm] Question about hardware LVM



On Thursday 02 February 2006 16:01, Ming Zhang wrote:
> linux seems can not handle the read_capacity data changed msg from san.
> so probably u will need to grow it, reconnect from linux, find the
> changed size, then run fs tools to grow it.
Neither can many other *nix hosts.  Usually growing is handled at the host 
level after the LUNs have been increased in size on the SAN.

> > I have been successfully using LVM on RedHat Linux Server with no
> > hassle. We are now deploying a $BIGVENDOR expensive FiberChannel SAN.
> > One of the main features of this SAN is that is able to grow a
> > filesystem
Not exactly your terminology is wrong here.  What you mean to say is that one 
of the main features of a SAN environment is that you can grow LUNs you 
present to hosts.

> > How does Linux handle this? Do I still have to use LVM? If I still
> > have to use LVM I do NOT see the point of "hardware base growing".
> > Simply, create a new LUN in the SAN and I can join to our LVM setup.
Well to put it bluntly no you don't need LVM just to grow a filesystem from a 
presented LUN on a SAN.  However if you'd like to use the SAN storage for 
many filesystems or as a way to offset local storage than you do need volume 
management.  Enter LVM.

Other considerations in this setup are growing filesystems.  These include 
JFS, XFS, Reiserfs and some consider ext3 capable for this job (it does have 
resizing tools check your distros docs).  If you need to shrink filesystems 
your only real option is Reiserfs.  I will not go into more detail about 
these filesystems, because you need to evaluate each systems needs and 
application requirements to determine a filesystem to utilize.  There are 
plenty of docs on the web with benchmarks and explanations of each.  Do your 
homework here this is important.

> > Maybe this is a "Storage 101" questio, but I do not fully understand
> > expensive SAN "hardware based"  filesystem grow.
This is Storage 101.  Something you must understand is that LUNs on a SAN 
might as well be hard disks in a server.  They are block devices that are 
underneath volume management that is also underneath filesystems.  You will 
have to maintain the systems on their own.  When a systems needs more space 
you grow the LUN, then you grow the volume under your volume management 
software (LVM here) then you grow your filesystem.  Read up on the tools you 
are using and get a firm understanding of how each one works in the ways you 
need.

I hope this sheds some light on what you are getting into.  SANs can be 
complicated.  Volume management can be a complicated subject.  However, you 
will have to understand how these fit together in your environment to make 
good decisions moving forward.
-- 
Zac Slade


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