Increasing drive capacity on NAS

Discussion in 'Mac OS X Server, Xserve, and Networking' started by davys, Jul 24, 2019.

  1. davys macrumors regular

    Mar 24, 2010
    Hello folks,

    Been happily running with the Western Digital 4 bay PR4100 for a couple of years now, with x4 3TB drives, Raid 5. I’m now down to just under 3TB of storage left, so I’m now thinking about increasing my capacity by adding two new Red drives, thinking about x2 6TB, to give new total of 18TB.

    Am I right in thinking that this is a straight forward process of just pulling two of the exisiting 3TB drives and replacing them with the two new 6TB drives, and that Raid 5 will just automatically re-build on the two new drives over a couple of days? Never done this before, so nervous as hell just thinking about it!

    Thanks in advance for any advice offered.

    Best wishes,
  2. chrfr macrumors 604

    Jul 11, 2009
    I'm not familiar with the Western Digital NAS, but unless it specifically offers a feature to allow expanding storage, replacing drives will not automatically add storage. Also, with RAID 5, if you pull two drives at once you will probably lose all your data. Be sure you have a backup before you do anything.
  3. davys thread starter macrumors regular

    Mar 24, 2010
    Thanks for the reply mate, advice much appreciated. I posted the same question on the WD forum, but no one appears to know there either so looks like I’ll have to contact WD support directly to get (hopefully) definitive advice. I can see how replacing two drives at once is not a good idea but hopefully there’s scope to replace one drive at a time with a higher capacity drive.
  4. Ledgem macrumors 68000


    Jan 18, 2008
    Hawaii, USA
    I don't use the Western Digital system, but I use a Drobo (five-bay system). The principle is the same with Drobo's system and RAID 5 either way: one drive can go down (or be pulled off), and when you replace it, the cluster will rebuild the lost data and spread it back onto the new drive.

    Drobo allows you to account for two drives going down at once, but it's not the standard configuration and takes more space to enable. I'd guess that the Western Digital system you're using is built to tolerate only one drive being taken out of the cluster at a time.

    What you can expect is this: probably safest to power down your Western Digital system, remove one old drive and replace it with a new drive, and then power it back up. The system should detect that something is missing, and begin the rebuild process. You will be able to access your data at this time but it's recommended to keep your usage to the bare minimum, because the rebuild process can take quite a while - possibly a day or two. Once the system has rebuilt and stabilized, do it again with the other drive you want to install, knowing that it's going to take another 1-2 days before the system re-stabilizes.

    It sounds like your data storage needs are pretty high... is a four-bay system really enough for you? You might want to look into upgrading further. There are eight-bay systems out there, and even more (although they get expensive). I liked one method that Synology offered, in which they made an expansion unit that can plug in to some of their other storage units, allowing you to plug in even more hard drives. Not sure if there's a performance hit with the expander versus just having one huge unit.
  5. hobowankenobi, Aug 8, 2019
    Last edited: Aug 8, 2019

    hobowankenobi macrumors 6502a

    Aug 27, 2015
    on the land line mr. smith.
    While some RAID arrays can expand a volume on the fly, many older and basic ones can't.

    As was mentioned, never pull more than 1 drive from any RAID. Technically RAID 6 (and a few others) can handle 2 drive failures at once...but I would be conservative and do 1 at a time.

    To be clear, with RAID arrays that can increase volume size on the fly and non-destructively, the process is usually:
    1. Pull a single drive; RAID volume will be in a degraded state
    2. Insert new/larger drive
    3. Rebuild volume
    4. Verify the array is not degraded; all drives are in use, no errors or warnings
    Once the volume is rebuilt and happy, proceed to next drive and repeat steps.

    To be clear, this is only a general guideline, and may vary by brand/model of RAID controller. One should always have a backup before starting. A damaged/corrupted RAID could be nearly impossible to recover data from.

Share This Page

4 July 24, 2019