[linux-lvm] Question about hardware LVM

[linux-lvm] Question about hardware LVM

[Javier de Miguel Rodríguez]

Hello

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

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.

Maybe this is a "Storage 101" questio, but I do not fully understand
expensive SAN "hardware based"  filesystem grow.

Thank you in advance

Re: [linux-lvm] Question about hardware LVM

[Ming Zhang]

i guess u can get that information from manual.

the hardware probably can grow the size dynamically. but it might still
depends on host to grow the fs.

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.

still, check manual is the way to go.

ming

On Thu, 2006-02-02 at 22:08 +0100, Javier de Miguel Rodríguez wrote:
> Hello
> 
> 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
> 
> 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.
> 
> Maybe this is a "Storage 101" questio, but I do not fully understand
> expensive SAN "hardware based"  filesystem grow.
> 
> Thank you in advance
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] Question about hardware LVM

[Zac Slade]

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

Re: [linux-lvm] Question about hardware LVM

[Ming Zhang]

On Thu, 2006-02-02 at 23:41 -0600, Zac Slade wrote:
> 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.

the point here is whether host can handle it on the fly, or need a
reboot&re-detect.


> 
> > > 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.

think so, unless some $bigname san is file system aware and can do that.
but i do not see any point to do that file system grow from a san point
of view. the sole purpose of san is to export a disk like device.

> 
> > > 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.

i think this is where to do volume management, or where to do storage
virtualization. if you use linux lvm, it is host based. if u use san
ability, it is array/san based.

> 
> 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.

if can grow the lun at san side, a linux lvm might not be needed. so the
layer is file system on top of san exported lun already.

> 
> 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.

ps, we still misuse LU and LUN. LUN = LU Number. so in most place, we
should use LU instead of LUN. but everybody know this, another storage
101.

ming