ReadyNAS NV+ Expansion

First posted on the 3rd September, 2011 – IT
Last modified on the 17th February, 2012, at 3:37 pm

Although I had planned to increase the size of my NAS’s array from 1.5 TB (4×500 GB) to 6 TB (4×2 TB) I had originally intended to only do this once I had upgraded my iMac to a 2TB disk. However, fait had other plans and one of my disk died a sudden death and now has major spin-up issues.

The positive is that I got lots of SMART errors a few days before so could buy four new 2 TB disks as planned. As the new disks have 4k sectors the usual RAID-X auto expansion trick is not possible and a factory reset is necessary to access the full capacity. However, this also wipes all data on the volume. Not great, but understandable as sectors are kinda important for RAID!

Most of my NAS is used for incremental backups, I can accept deleting this data as I have an offsite backup via CrashPlan. There was, however, about 80 GB of assorted stuff that I only had stored on the NAS that, although not impossible, would be time consuming to re-collect. Although I have an old external disk that I could use to store this data I could not access the data with one disk down. This was because when a disk in the array fails the NAS shuts down automatically, and unmounts the volume to limit possible further irrecoverable data loss. So how to get my data off the array? I didn’t particularly want to but another 500 GB disk gust for this one task. With four new 2 TB disks with 4k sectors I thought I would give one of them a go, as the advanced format functionality is ment to offer transparant mimicing of a 512 byte sector disk.

Pluged it in, re initialised disk, re-synced array and voila my data was back!

From here everything was easy:

  1. download data
  2. backup config
  3. swap out remaining 500 GB disks for other 2 TB disks
  4. do factory reset
  5. initilise array
  6. reload config
  7. apply Lion Netatalk settings for Time Machine
  8. upload data

To get Time Machine working again on the NAS a few more tricks are needed. Previously the disk image on the NAS was named according to the MAC address. Thus to limit backup size per machine you just needed to crate a sparse disk image with fixed maximum size and rename it accordingly.


hdiutil create -size 1t -fs HFS+J -volname "Backup" /Volumes/Backup/-.sparsebundle

This approach allowed me to limit the size of the Time Machine backups on a per machine basis. Having expanded my NAS to 6 TB I want to use 4 TB to backup my iMac and 1 TB to backup my Laptop.

However, it would appear that in Mac OS 10.7 does things slightly differently and ignores the size-limited image and goes ahead and creates a new image anyway. The sparse bundle created by Time Machined is also just named after the machines name and the name no longer includes the MAC address. Digging inside the two sparsebundles reveals that the sparsebundle created by Time Machine has two extra files:

com.apple.TimeMachine.MachineID.bckup
com.apple.TimeMachine.MachineID.plist

Simply coping these files from the Time Machine created bundle to the size-limited bundle and delete the Time Machine bundle.

Upon starting a backup Mac OS X warns that the disk has changed and asks if you want to use the new disk. Upon saying yes to this everything proceeds as normal and the size limited sparse bundle is used.