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Yukimura
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Joined: 25 Aug 2006
Posts: 163
Location: Slovenia

PostPosted: Thu Nov 12, 2015 12:14 pm    Post subject: New install with ssd and 3 hdds, need sugestions on how to s Reply with quote

Hello fellow Gentooers,

I currently have a system with 1 SSD drive and 2x2TB hdd drives (using software raid1), using bcache and on top of bcache I'm using BTRFS. Now I recently started getting unrepairable errors by btrfs scrub utility (and the system is only 2 or 3 months old). After doing some research, I figured out bcache and btrfs don't really like each other and they can leave you with this unrepairable errors.

So I'm thinking of reinstalling the whole system, but can't figure what would be best use of my hardware. I have 3x2TB hdds available and I would like to use BTRFS on them and use BTRFS's raid1. But how can I use SSD with this setup? I'd really like to have it as caching device.

All your suggestions will be of great help.

Thanks!
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frostschutz
Advocate
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Joined: 22 Feb 2005
Posts: 2970
Location: Germany

PostPosted: Thu Nov 12, 2015 12:20 pm    Post subject: Reply with quote

Quote:
Now I recently started getting unrepairable errors by btrfs scrub utility (and the system is only 2 or 3 months old).


8O

Quote:
I'd really like to have it as caching device.


You could go to FreeNode #btrfs and ask them what works for SSD caching with BTRFS.

I don't use my SSD for caching, I just put / and /home on it (that's everything that should be there, really), and put the clunky stuff on HDD. There's no point caching a movie or whatever.

It's only a 64GB SSD but even so that's plenty for system, home, mails, git projects, ... on a database server it might be different but on a regular desktop you don't have that much data that needs to be fast and even if you did SSD nowadays are more like 256G so that's not a problem either. Caching seems like a crutch to me in comparison, the idea is nice but if introduces dangers of filesystem corruptions, thanks but no thanks.

My HDD even are in standby most of the time as long as I'm only working on the SSD side of things. I don't think that would be possible with generic purpose caching, it never caches everything.
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krinn
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Joined: 02 May 2003
Posts: 7071

PostPosted: Thu Nov 12, 2015 12:29 pm    Post subject: Reply with quote

If you want performance and keep some safety, use the ssd with bcache, with a power inverter to avoid power lost while the ssd is still holding datas and a real FS that is known to be stable.

Keep searching, you will see the list of what btrfs doesn't like is bigger than what you think (and that you don't even need anything that btrfs wouldn't like to have trouble with it).
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