Process for expanding Snapshot RAID DRU & PPU size

This tutorial is only for users running a Snapshot Configuration in Expert mode only

Paths in this tutorial are purely examples and you should refer to you own mount points

With FlexRAID, the PPU must be at least as large as your largest DRU.

So you have set up your FlexRAID and everything is humming along nicely until one day you want to put a larger DRU in, but this would require a larger PPU as well. What will happen to all of the existing parity data? Do you need to re-create the RAID? Short answer: no.

FlexRAID allows you to migrate the existing parity data, and as FlexRAID is based on simple drive paths, you can do a simple switch of the old PPU with the new PPU.

The process is as follows:

1. Install your new drives and get them ready for use
2. Copy PPU data from your existing PPU to your new larger PPU
3. Turn off Flex services
4. Unmount existing PPU
5. Mount new larger PPU to the same path as the prior PPU
6. Mount new larger DRU
7. Turn on Flex services
8. Run quick validate; confirm all OK
9. Add new DRU path via Data Configuration tab in UI RAID configuration
10. Run an Update
11. If using the View, add the new unique volume to the View config & republish
12. Done

As an example, I am about to do this in my setup at home. The scenario is:

At the moment all my DRUs and PPU are 2 Tb. I want to introduce a 3 Tb DRU, thus I will need a 3 Tb PPU as well, and I will free up the existing 2 Tb PPU to be part of the storage pool instead.

1. Copy PPU data from 2 Tb unit onto 3 Tb drive
2. Turn off Flex services
3. Unmount 2 Tb from C:\Mount\Parity01
4. Mount 3 Tb PPU with the old 2 Tb path (C:\Mount\Parity01)
5. Mount new 3 Tb DRU with new path (C:\Mount\Disk06)
6. Mount old 2 Tb PPU (to be a DRU) with new path (C:\Mount\Disk07)
7. Turn on Flex services
8. Run quick validate; confirm OK
9. Add new DRUs (Disk06 & Disk07) paths via Data Configuration tab in UI RAID configuration
10. Run Update
11. Add 2 more unique volumes to View config & republish
12. Done – should have an additional 5 Tb of space in the pool

Be Sociable, Share!



8 Responses to “Process for expanding Snapshot RAID DRU & PPU size”

  1. harlockpt October 17, 2011 at 11:08 AM #

    In your scenario I can assume that you could just buy one 3TB HDD and put it as the new PPU and reuse the old 2TB PPU as a new DRU thus increasing the storage in 2TB..


    • webs0r October 17, 2011 at 4:22 PM #

      Yes that would work.
      But then there is no reason to get a 3TB at all, except for future-proofing (you can wait longer before nabbing the other 3TB for your DRU and save a few extra $$).

      • harlockpt October 18, 2011 at 8:14 AM #

        Yeap, unless you have your slots full and want to increase capacity.
        If you have a small case and it’s full with 2TB HDD’s in that situation you MUST buy two 3TB HDD.
        One to act as the PPU and the other one to effectively increase the capacity in 1TB.

        So you would replace 2x2TB with 2x3TBs to have a 1TB increase :(.

        That brings one question.. In this situation where you have no space for new disks what is the best approach to replace a disk?
        Put the new HD as PPU and rebuild the PPU and later replace a DRU and rebuild again?

        • webs0r October 18, 2011 at 8:31 AM #

          I think the best approach is to build another server or expand your existing somehow (controller with external SAS connection).

          Hm I would suggest planning your approach step by step.

          You could disconnect 2 other DRUs, insert the 2 new disks and:
          – migrate the DRU data to the new bigger DRU
          – copy the PPU data onto the new bigger PPU
          – replace the DRU/PPU drives with the new ones & do the drive mount point switch
          – reinsert the disconnected DRUs
          – check via Flexraid update/validate/verify everything went OK

          Seems like very little gain though and getting more slots should be the priority instead.

  2. Roland May 17, 2012 at 9:02 PM #

    I have 6 x 1TB disks, I’d rather replace them, as they are small.
    But I’m wondering how many disks I can have as DRU with one PPU?
    Example: I will put a 3TB PPU in and create out of all disks I have 3TB DRUs. That could be 8 or 9 x 3TB DRUs.
    Isn’t there a limit on how many or can I just add more DRUs with 3TB while keeping one PPU with 3TB?

    • webs0r May 21, 2012 at 2:03 AM #

      Hi Roland,

      You can have as many DRUs to 1 PPU as you wish.
      However you get to a point where the risk of a single drive failure increases to a point where you want more protection. Depends on how risk averse you are.

      For me, I am planning to create a 2nd snapshot RAID set after 11 DRUs. So that is – another PPU supporting a new set of DRUs. I prefer having 2 RAID sets as I know that my first RAID set be pretty much static. This will decrease update loads on the initial set as I may only run Updates every month or less on that set of data.

  3. Dutch June 8, 2012 at 3:54 AM #


    Why not just use smaller partitions ?
    You can draw more partitions into 1 dru, this is also valid for the PPU.

    Lets say our smallest disk is 500GB and i have this hardware:
    2 500GB
    1 1000GB

    so if i now make 2 partitions on the 1000GB drive and and them bove as DRU.
    I can use the both 500GB disk (both own partition) to create the PPU for the pool right.

    Or do i see something wrong ?

  4. Terry October 14, 2015 at 10:35 PM #

    Would this set of instructions work in Cruise Control as well? I use snapshot raid in cruise control mode (I think).

    I want to replace a single 2 TB PPU with two 4 TB PPUs (so that I can expand all of the DRUs to 4 TB each over time). Should I use these instructions, or should I delete and re-create the configuration?


Leave a Reply