Raid 1 used drive insertion, which drive will be the master for the rebuild?

PaulPlasmar Posts: 2  Freshman Member
edited July 2018 in Personal Cloud Storage
I have a NSA320 raid 1 setup. A while back I took 1 drive out for offsite storage. Inserted a new drive and the raid rebuilt properly and has been working fine. Now I want fresh snapshot offsite so I want to take a drive out to put it offsite but I dont want to buy another drive. I want to put the old offsite one back in and have it rebuild over the old data. I am worried it will pick the old data as the master for the rebuild. I dont want to pull all drives and format the old. Will it work automagically or will I have to take the time to format?


Accepted Solution

  • Wiasouda
    Wiasouda Posts: 156  Ally Member
    Accepted Answer
    You have A, B and C disk, then A and B already in NSA320 with RAID 1, then you pull out B, and inserted C to the NSA320, then rebuild done and works fine, but now you want to put the B back to NSA320 to swap C, am I right?

    Since C disk already been rebuild to NSA320's RAID and the record A and C is RAID 1 group in NSA320, if you put the B back and without disk format, then NSA320 will not identify it and sync as RAID 1 disk, therefore, you have to move out the new data from your B and format it, then put it back to NSA320

All Replies

  • Mijzelf
    Mijzelf Posts: 1,559  Guru Member
    The raid header on the disk contains a timestamp of the last write. If two raid members have a different timestamp, the array is considered degraded, and the 'oldest one' is not assembled in the array. So re-adding it would cause a full sync.
    So if you shutdown the 'backup', and then do a write to the 'original', before shutting it down, the 'original' master should be used. (Assuming the clock is right on both systems).

    However, this is a bad idea. Raid is on a lower level than the filesystem, so all diskspace will be synced, even the unused space. And that will happen twice, if you put back disk 'C', as @Wiasouda calls it, it will also need a full sync, as the array has changed, meanwhile.
    So your 'swap twice' will keep your NAS busy for days.

    You'd better use a normal backup method.
  • PaulPlasmar
    PaulPlasmar Posts: 2  Freshman Member
    Disk B has been in a fireproof safe for a month and its data is now considered stale and unwanted so there is no 'twice' unless you consider next month. I want to pull C and put it in the fireproof safe and bring B up to A's current state so I was hoping the rebuild would happen A to B and not B to A. I appreciate the insight about syncing unused space not a huge issue but it looks like just to be safe I should format be before rebuild. I was hoping that if I kept drive A in the left slot which appears to be DriveSlot0, that the rebuild would always happen with it as the master and DriveSlot1 the slave. Its a pain to reboot and remote into it just to format and reboot again to put Drive A back in. Thank you both!
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