Re: Hot data tracking / hybrid storage

[Ferry Toth <ftoth@exalondelft.nl>]

Op Mon, 16 May 2016 01:05:24 +0200, schreef Kai Krakow:

> Am Sun, 15 May 2016 21:11:11 +0000 (UTC)
> schrieb Duncan <1i5t5.duncan@cox.net>:
> 
>> Ferry Toth posted on Sun, 15 May 2016 12:12:09 +0000 as excerpted:
>> 
<snip>
> 
> You can go there with only one additional HDD as temporary storage. Just
> connect it, format as bcache, then do a "btrfs dev replace". Now wipe
> that "free" HDD (use wipefs), format as bcache, then... well, you get
> the point. At the last step, remove the remaining HDD. Now add your
> SSDs, format as caching device, and attach each individual HDD backing
> bcache to each SSD caching bcache.
> 
> Devices don't need to be formatted and created at the same time. I'd
> also recommend to add all SSDs only in the last step to not wear them
> early with writes during device replacement.
> 
> If you want, you can add one additional step to get the temporary hard
> disk back. But why not simply replace the oldest hard disk with the
> newest. Take a look at smartctl to see which is the best candidate.
> 
> I went a similar route but without one extra HDD. I had three HDDs in
> mraid1/draid0 and enough spare space. I just removed one HDD, prepared
> it for bcache, then added it back and removed the next.
> 
That's what I mean, a lot of work. And it's still a cache, with 
unnecessary copying from the ssd to the hdd.

And what happens when either a hdd or ssd starts failing?

> --
> Regards,
> Kai
> 
> Replies to list-only preferred.