Thanks for reply Eric.

That sounds quiet dangerous to risk 8TB of production data. I guess the 
only safe way is re-formating the partition and therefore it would mean 
8TB copied-out then copied back in which imposes a longer downtime to 
the server.

Best regards
Fernando


On 26/06/2017 14:58, Eric Wheeler wrote:

On Mon, 26 Jun 2017, FERNANDO FREDIANI wrote:

quoted

Hello folks.

I have been using Bcache in a server in production with pretty good results so
far.

Now I am looking to add it also to another server that is suffering from disk
I/O. However this server in question has a fairly large storage running (circa
8TB of used data) and therefore stopping it for a long period becomes
difficult.

Question is: Can I add an SSD and Bcache to this server and use it for the
existing 8TB filesystem ? If so when I run make-bcache -B /dev/sdx1 to create
the backing device will it not overwrite what is currently on /dev/sdx1 ?

Not officially.  The bcache superblock is in the first 8k of disk (by
default, but can align the payload) so 8TB would need shifted right
assuming the right-hand-side has room to grow.

Disclaimer: this could be dangerous, so at your own risk:

While I've not tried this, theoretically you could put dm-linear atop of
the bcache bdev and prepend some metadata area, using the `--data-offset`
parameter in make-bcache as the start of your data area.  Be sure to test
on something non-critical if you go this route and make sure the sector
math is correct or risk damaging the front of your 8TB volume.  If you go
this route and it works, please report back with what you did!

--
Eric Wheeler

quoted

Thanks
Fernando
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html