Smart Array Array Expansion

[Steve Cavendish_1]

I have a question regarding expanding an array set and logical volumes under that array set. I have a customer who created multiple logical volumes under a single array group. I know this is not the best way to do it but it was done. What I am not sure is whether or not I can now expand the logical volumes under the set. Has anyone done this? if so, did it work? I would test but my test box is being used for the next couple of weeks.

Any help as always will be greatly appreciated.

Steve

P.S. This thread has been moved from HP 3PAR StoreServ Storage to ProLiant Servers (ML,DL,SL). - Hp Forum Moderator

[Arch_Muthiah]

Steve,

From google....

Physical Drive Concatenation:
-----------------------------
One method for increasing available capacity for an application is to expand the size of the
physical redundant array of independent disks (RAID) set (which equals the logical volume) by
concatenating additional disks into the set. Compaq pioneered this approach in the mid-1990s for
its host-based Smart Arrays and, as a result, invented the concept of dynamic volume expansion.
The disadvantage of the approach, especially with today's disk drives, is that the increments of
expansion are limited to physical disk size and it assumes that additional drives may be added to
the array. A further disadvantage is that, unless the logical volume is equivalent in size to the
RAID set, the logical volumes may not grow in size, even though the RAID set does.

Logical Volume Concatenation
============================
A more-flexible option is for the array (with the storage administrator's approval) to concatenate
an additional volume into the RAID set and then re-cut the logical volumes on the fly. This
happens transparently while the volumes are online, but, at the end of the process, the
application sees a larger volume. With a straight concatenation process, data flows from one
logical unit number (LUN) to another as space is required, filling up one after another until the
new, larger volume is full. With this method, the concatenated LUNs can usually be different sizes
and perhaps even different RAID levels from the original LUN. Most host software, such as
Veritas Volume Manager, can handle this process without user intervention. Others, such as
Solaris require a simple dismount and remount of the volume. This short (five- to 10-second)
process requires no data movement or system reboot, but the application will be denied access to
the volume during that time. However, some older operating system versions, such as Windows
NT 4.0, may require some manual reconfiguration by the storage administrator, followed by a
reboot.


Archunan

[Arch_Muthiah]

Steve,

From google....

Logical Volume Concatenation Plus Re-stripe:
============================================
When high performance is required in addition to a larger volume, a concatenation plus re-stripe
methodology is preferred. After expanding the original volume with additional logical volumes
(creating what EMC calls a MetaLUN), data is re-striped across the larger entity. This process
takes longer than a straight concatenation of logical volumes, but if the concatenated LUNs are
located on different physical disks, the user also achieves better performance because of the
multiple spindles. Caveats for this method may include restrictions, such as the requirement that
all LUNs must be the same size and the same RAID level to be concatenated and re-striped (for
example, CLARiiON). Others have the flexibility to build volumes virtually and expand to any size
(such as Xiotech). EqualLogic goes one step further by allowing the stripe to be expanded and
built across multiple nodes in its grid. In HP's Enterprise Virtual Array (EVA), the organization of
volumes as thin slices across disks allows the volume to be expanded simply by adding a slice.
This means that the EVA does not have to go to the extra work of re-striping after concatenation.

Thin Provisioning
==================
The ultimate in dynamic volume expansion is thin provisioning, a method originally pioneered in
the early 1990s by StorageTek in what is now called the FlexLine V2X2/V2Xf Shared Virtual
Array and otherwise only offered, as far as we know, by 3PAR on its InServ Storage Server and
Network Appliance on its fabric-attached storage (FAS) line. IBM has announced its intention to
support thin provisioning on its TotalStorage DS6800 and TotalStorage DS8000 arrays, but it has
not provided a time frame for this additional support and the capability is not yet shipping. Thin
provisioning is essentially the virtualization of giant logical volumes at the outset, so that logical
capacity is always sufficient to meet an application's needs. Physical capacity, however, is only allocated on an as-needed basis, drawn from a pool of all the unused physical capacity in the
array. Thin provisioning provides the simplest and most-flexible method for dynamically
expanding volumes today.


Archunan

[Arch_Muthiah]

Steve,

You can find good info on how to expand the logical (multiple) volume.

http://www.informit.com/articles/article.asp?p=359414&seqNum=3&rl=1


Archunan

[Arch_Muthiah]

Steve,

Using array configuration utility (ACU), you can expand the capacity or you can extend the volume.

This explains in details about ACU.
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00257511/c00257511.pdf

Archunan

[Steve Cavendish_1]

Thanks for responding, I am very well versed in the different ways to expand the size of volume. What I was lookg for in particular was on Smart Array Technology. Specifically whaen more than one logical volume is definedunder a single array group. I was able to free up my test server and try it out. It worked perfectly. I was able to add a second pair of hard drives to an existing pair, expand the array, then extend each logical individually under it.

Thanks again for the replies.