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My companies Synology NAS (DS1618+) has 6 12TB drives in a RAID5 array. One of the drives went from abnormal to failing. We do not have a "hot spare". Co-workers depend on this on a daily basis so I guess my question is, are we looking at any downtime after replacing the drive? It is my understanding the new drive can be populated while the system is still operation or is that false? I found plenty of information on how to do this, but none on the ramifications.

Before you ask, yes we do have a backup.

In case it matters, we have a capacity after RAID and formatting of 34TB and we only use 18TB.

Alex
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  • I posted this answer long ago. It may be something you want to look into before going about trying to rebuild. [RAID 5 Array: Probability of Failing to Rebuild Array](https://superuser.com/questions/1334674/raid-5-array-probability-of-failing-to-rebuild-array/1334694#1334694) If you have good drives it probably won't be an issue, but you should know your chances before going all in. – DrZoo Nov 18 '20 at 05:13
  • We have 6 ST12000VN0007-2GS116 if that helps. The one that is throwing errors has a bad sector count of around 60k. This is all a bit over my head haha. Our IT guy ain't great so i'm just trying to make sure nothing comes back and bites us. my biggest question is regarding downtime while the RAID (rebuilds), and mainly if there is any? – Alex Nov 18 '20 at 05:20
  • I think with RAID 5 you can use your drives while it's rebuilding, but it would obviously decrease the the performance of the drives while rebuilding. The rebuild time could be a while, based on what [Server Fault](https://serverfault.com/questions/967930/raid-5-6-rebuild-time-calculation) says I think your biggest question should be the success of rebuilding. With your setup you have a 61% chance of a successful rebuild. If a second disk fails, you are in a heap of trouble. – DrZoo Nov 18 '20 at 05:45
  • It would require some planning but I would look into trying to convert to RAID 10. – DrZoo Nov 18 '20 at 05:52

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