Re: Hot data tracking / hybrid storage

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

Am Sun, 15 May 2016 21:11:11 +0000 (UTC)
schrieb Duncan [off-list ref]:

quoted

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

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