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Should I move away from MDADM & LVM?
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Joined: 27 Apr 2014
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PostPosted: Tue May 06, 2014 9:47 pm    Post subject: Should I move away from MDADM & LVM? Reply with quote

I'm testing out new methods for my home-made NAS. The tried and tested method for creating a software RAID set is to use MDADM -> LVM -> FS. For my current filesystem I chose XFS in the past. Of course, it is highly advised to perform regular RAID scrubbing through a cron job.

However, after reading up and realizing that even a major NAS like Netgear's ReadyNAS is now using BTRFS, I'm starting to wonder if maybe I should switch to other structures.

For example, both BTRFS and ZFS are capable of creating not only their own RAID sets, but also create their own logical volumes, thus replacing both MDADM and LVM. But ZFS is still experimental in Gentoo, and the RAID features of BTRFS are considered in beta-stage. ZFS has deduplication, BTRFS can defragment.

Considering that it's quite difficult to change the underlying structure once my data is on there, I'm hoping to gather some opinions here.

Should I continue to rely on MDADM, or will a ZRAID for example be better (maybe it has better scrubbing)? Should I continue to use XFS or is for example EXT4 or BTRFS a better system? If BTRFS is a recommendation, should I use its built-in volume management?

As for my requirements, I don't have a backup beyond this (simply too much data to back up in a home system), so I need good redundancy (currently I'm running on a RAID6 volume). I may or may not use a crypto-layer for parts of it. Performance isn't high on my list, as long as I can get to my data. Although I may at some point stream my audio/video from it.

So I'm hoping for some veteran advice here. Thanks!
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Joined: 05 Oct 2005
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PostPosted: Sat May 10, 2014 5:31 am    Post subject: I've moved away from mdadm Reply with quote

I've moved away from mdadm in the past year and now am on btrfs based volumes for all of my mirrors and raids and just about all of my system drives. The only place I haven't had success with btrfs is using it to replace squashfs on thinclient drives where I only have about 1gb of space to work with. The stability appears to be there, and now development is starting to look at performance. The snapshot capability works great, but I have yet to look into using it to do incremental rsync to a remote site. There was a writeup in Linux Journal or somewhere about that when the journalist was covering btrfs. Since its COW based, there's also something in sourceforge somewhere to do manual de-dedupe, but I haven't looked at it yet. Most of what I care about dedupe wise gets handled by snapshotting of my VM's.

The only thing that has bitten me is a system where the memory wasn't quite reliable, and memory errors eventually caused filesystem problems. The fsck isn't quite there yet, but I was able to copy the good stuff around the bad stuff (filesystem goes into readonly mode). Do redundancy on more than one server and you won't have a problem for your crucial stuff.

It's nice to see stuff in your dmesg when btrfs decides to correct a bad spot in a raid set when the underlying drive is on the verge of doing a whig out or bad block replacement.
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