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Old 11-25-2018, 09:16 AM   #1
road hazard
Registered: Nov 2015
Posts: 145

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Question ZFS or BTRFS are only options for faster re-silvers of RAID disks?

Currently using Mint 19. I picked up some more WD 8TB easystore drives from Best Buy recently, they were on sale for $130. I'm currently testing the surface for errors before adding them to my existing RAID 5 array. Once I add them, I know it will probably take over a week of non-stop drive access until the array is rebuilt but re-silvers on 8TB drives are SSSLLLOOOWWW with MDADM.

Sure, I could use ZFS or BTRFS since they only copy parts of the drives that contain data vs. block copying like MDADM but with Mint being a point release, packages only get updated every few years.

BTRFS is still undergoing massive re-writes and I'm sure whatever version of BTRFS in Mint will quickly grow old and still have those bugs. Plus, I hear that RAID5 on BTRFS is just a complete mess and not to be trusted. My PC is on a UPS and it just runs a Plex server and I can't remember the last time I had a kernel panic and the system froze... maybe I'll be OK?

As for ZFS, I'm not worried about using non-ECC memory but I am worried about RAM usage. I don't care for snapshots so that feature will be turned off but what about the version of ZFS in Mint 19? Any horrible, data killing bugs I need to know about? My main array is 40TB and the backup array is going to be 40T (once those 2, 8TB drives are added) so will 16GB of RAM and ZFS handle that? I know that with existing versions of ZFS, if I want to expand the pool, I need to add twice the hard drives before I can expand but I'm totally fine with capping out at 40TB. That should hold me for a couple years. Not worried about what to do after that as I'll outgrow my case anyway.

TLDR: Using Mint 19. Main array is 40TB, backup array will soon be 40TB. Hate slow re-silvers so should I use BTRFS, ZFS or stick with super slow (but reliable) re-silver times on good old MDADM?
Old 11-27-2018, 07:28 AM   #2
Registered: Aug 2018
Location: Atlanta, GA - USA
Distribution: CentOS 6-7; SuSE 8-12
Posts: 599

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I've a software RAID 5 with 4 x 8TB drives (Hitachi drives). This is on CentOS 7.5
Changing the values in /proc/sys/dev/raid/speed_limit_min and /proc/sys/dev/raid/speed_limit_max made a significant difference in resync (completes in few hours instead of days).


btrfs, mdadm, zfs

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