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I have a DS220+ with 2 identical drives, configured as RAID, so just one volume. Everything was working great, but to access the new object-recognition in photos, I added RAM, which caused some corruption and now the volume is read-only and won't repair itself (even after removing the RAM). So now I'm preparing to do an external backup and rebuild the NAS. But now I'm wondering: If volume issues are more likely than drive issues, should I forget about RAID, create one volume on each drive, and use the second volume as a local backup? Or is RAID still the best first line of defence? (Or is there a way I can do both with two drives?

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[–] [email protected] 2 points 1 year ago (6 children)

Get another hard drive and do RAID5. Then you get striping AND parity.

Or even better, get TWO more drives and do RAID10.

I’ve got 8 SAS drives in a RAID10 and it’s lovely.

[–] [email protected] 2 points 1 year ago* (last edited 1 year ago) (4 children)

RAID is something I haven’t learned yet but really should.

My server has 4 4TB hard drives. Sounds like I could do RAID10 and only have 4TB of storage. Or RAID5 and 8TB?

Right now I have no raid. 1/4 of my hard drives has about 700GB of data and is movie and shows. 2/4 hard drive has 91GB and is photos and cloud data. 3/4 is blank and 4/4 is borg backups from my desktop and server and second hard drive currently at 120GB. My media drive has no backups right now and is not really being used.

It sounds like I could put all of my data on hard drive 1 which will only be about 1TB and then have RAID so that data is secure.

I would like having 8TB storage with raid 5. But maybe raid 10 is smarter and if I want more storage I’ll have to get more drives.

[–] wth 2 points 1 year ago

Be wary of RAID 5 or 6.

They both have a « write hole » problem (or though much less so in RAID 6). Any power failure which causes an incomplete write can cause a complete RAID corruption - meaning all data is lost. Hardware RAID controllers usually have an onboard backup battery so they can store some information to complete operations should there be a sudden power failure. Software RAID does not have this, and you need to provide a UPS with automatic clean shutdown as the battery runs low using nut or some equivalent.

Some people go as far as to say that RAID 5 should never be used.

You also have very long recovery times when you replace a failed drive (days). Any other failure during this time means total data loss (of course RAID 6 gives you a second redundancy). Weekly Resyncs are very slow too (hours to days), and (unless you constrain your max throughput) will bring your system to its knees.

zfs does not suffer from these problems, BTW.

I run software RAID 5 via mdadm and have a UPS. I’ve replaced drives twice with no issues other than a slightly nervous long wait during recovery. I’m too cheap to buy the extra HDD for RAID 6, and may end up regretting it one day.

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