EMC VMAX – Disk Group & Pool Expansion

In order to expand a VMAX Thin Pool we must first create the additional Data Devices (TDATs) on the underlying physical Disk Group. This example outlines how to calculate and create those TDAT devices and then expand the Thin Pool with the newly created TDATs.

Scenario:
A Disk Group that consisted of 64 X 600GB disk drives has been increased to 128 X 600GB Drives. EMC will be required to create and apply an upgrade BIN in order to expand the existing DG to 128 Disks, once this has been completed we can then proceed with the TDAT configuration.
After gathering the details with respect to the existing Hyper and TDAT sizes, then we can do a quick calculation in order to determine the count and size of the TDATs required (In this case the configuration is a simple replica of the existing configuration).

Calculating the Hyper Size
If we take the scenario above where a 64 Drive DG has been doubled to 128 Drives, with each of the first 64 drives in the DG having 8 Hypers per disk in a RAID 5 (3+1) configuration.

Listing the existing TDATs within Disk Group 1:
symdev list -disk_group 1 -datadev

From the output of this command we can see that the TDAT size is 206130MB, from this we can calculate the Hyper size used:
206130/3
=68710 MB Hyper Size
Hypers

Calculating the number of TDATs Required
TDAT
From the image above you can gather that for each set of 4 Drives (Raid5 3+1) we require a total of 8 x TDATs.
8 Hypers * 64 Disks
=512 Hypers
=512/4 (R5 3+1)
=128 TDATs

Creating the New TDATs
Creating the new 128 x TDATs required on the newly added 64 Disks:
symconfigure –sid xxx –cmd “create dev count=128, config=Raid-5, data_member_count=3, attribute=datadev, emulation=FBA, size=206130 mb, disk_group=1;” Preview -nop

symconfigure –sid xxx –cmd “create dev count=128, config=Raid-5, data_member_count=3, attribute=datadev, emulation=FBA, size=206130 mb, disk_group=1;” Commit -nop

New TDAT Range Returned = 1177:11F6

List the new TDAT range created:
symdev list -datadev -disk_group 1 -nonpooled

Adding the new TDATs to the Thin Pool
Adding and enabling the new TDATs to the existing pool and thus essentially doubling the capacity of the Pool:
symconfigure -sid xxx -cmd “add dev 1177:11F6 to pool ‘Pool-Name’ type=thin, member_state=enable;” Preview -nop

symconfigure -sid xxx -cmd “add dev 1177:11F6 to pool ‘Pool-Name’ type=thin, member_state=enable;” Commit -nop

Rebalance the Pool
This command will rebalance the allocated extents in the Thin Pool nondisruptively across all of the enabled data devices in the pool. Automated pool rebalancing should be run whenever new data devices are added to a pool.
symconfigure -sid xxx -cmd “start balancing on pool ‘Pool-Name’ type=thin;” commit -nop

Check on the rebalancing progress:
symcfg -sid xxx -pool ‘Pool-Name’ verify -poolState -balancing

Display a detailed report of the expanded Pool
symcfg show -pool ‘Pool-Name’ -thin -detail -all -mb | more

The pool now consists of 256 TDATs (or 1024 Hypers!)

13 thoughts on “EMC VMAX – Disk Group & Pool Expansion

  1. Hello dave,

    Could you please give insight on aclx devices? And its differences with gatekeeper devices.

    Thanks, Lejy philip

    Sent from my iPhone

    >

  2. Dave,

    Nice article.

    The word here should be “Add the new TDATs to the Thin Pool” instead of “Bind the new TDATs to the Thin Pool”.. we bind tdevs to a pool and add tdats to a pool.

    Thanks!

  3. hi Dave,
    could you please help me understand if pool rebalancing can cause performance issue?
    If i add new data devices to the thin pool, does it automatically starts rebalancing or we need to explicitly run the pool_rebalance command ?

    • Rebalance the Pool
      This command will rebalance the allocated extents in the Thin Pool nondisruptively across all of the enabled data devices in the pool. Automated pool rebalancing should be run whenever new data devices are added to a pool.
      symconfigure -sid xxx -cmd “start balancing on pool ‘Pool-Name’ type=thin;” commit -nop

      Check on the rebalancing progress:
      symcfg -sid xxx -pool ‘Pool-Name’ verify -poolState -balancing

      • Workload performance maybe impacted depending on how the system is loaded at the time. Please carry out the required analysis before proceeding.
        Thanks

  4. Hi David,

    We are getting SATA, FC and EFD drives added to our VMAX40K system tomorrow. Can I run rebalance on all 3 thin pools afterwards or should it be one at a time (waiting until the first pool completes)?

    Thanks!

  5. Hi David ,

    It is a very nice article , Is there any way we can know more about adding disks to the existing Disk group and making changes in the bin file ?

    Regards
    Anil

  6. Thank you David , Change was finished successfully completed and you article helped me a lot , As a consultant I frequently attend interviews and your site always helped me .

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