Replace bad HDD of Synology NAS DS412+ on DSM 5

TL;DR

Replacing 1.5 TB drive with 4 TB took 10 hours for 4.5 TB used on 5.5 TB SHR array

Background

  • information collection
    • max supported storage: 16 TB (4 TB in each 4 bays)
    • latest DSM version: 6.0 is out (I postponed to update after replacing HDD)
    • RAID calculation: existing 1.5+2+2+2 = 5.5 usable to 2+2+2+4 = 6TB usable (SHR1)
    • determining HDD brand: WD Green & Seagate Barrucada available and I chose Seagate as WD green’s head parking cause problem for NAS
    • SMART attribute: I have non-zero nubmers under Reallocated Sector Count & Drive Reconnection Count & and everyone suggested Reallocated Sector Count should be zero (and if non-zero, backup data and replace ASAP)
  • getting compatible disk model – check this page before buying
  • deciding which HDD size to buy (using RAID tools) – this calculator can show how much disk space will be used or unused (make sure to read instruction before you buy HDD)
  • reading instruction – Synology KB has complete instruction on how to perform. Left it open to read while you are performing the steps.
  • buying – bash out the money, check physical defect and warranty period
  • physically replacing – note which bay to eject, shutdown, eject bay, replace HDD, insert bay, restart, then disable beep (if beeping)
  • repairing – inserted HDD is uninitialized. Initialize and repair the volume group.
  • expanding – depending on the size of newly inserted HDD, you might need to expand the volume. Mine can expand another 500GB. It took less than 1 minute to expand.
  • pricing calculation 44 MMK/GB

Other things I learnt

  • SMART Value means normalized Value and it should be greater than Threshold number
  • For reallocated sector count, not only the number but also the rate of increase in number is important.
  • I had 2 (out of 4) HDD having non-zero reallocated sector count.
    1. 1.5TB with lower number but much higher power on hour
    2. 2TB with much higher (4 digit within 4 months)
  • Contrary to theory I learnt, I changed the 1.5 TB with 4TB. Now I am running with those 4 digit sector count.
  • SHR1 can accept one drive failure
  • SHR2 can accept two drive failure
  • make sure you use Uninterruptible Power Supply during repairing
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