Is there a "nossd" option ?

Is there a "nossd" option ?

[Swâmi Petaramesh]

Hi,

Running a 3.19 Ubuntu kernel,

I'm currently budling a RAID-1 BTRFS set for which every underlying device is 
a LUKS-encrypted device itself built out of a bcache device comprised of a 
mechanical HD partition + an SSD cache partition.

Looks like it's working.

BUT I see that BTRFS decides by itself to mount with the "ssd" option as  
bcache makes it think the device is not "rotational".

However I feel that a mechanical HD plus SSD bcache should probably not be 
"SSD-optimized" as the underlying storage is indeed mechanical and bcache 
already manages the SSD part optimization by itself - and I'm afraid the "SSD 
optimization" could actually cause the mechanical storage to end up being much 
more fragmented than it should...

So the question is : Is there a mount option such as "nossd" that I could use 
to inhibit the automatic SSD "choice" that BTRFS makes ?

TIA, kind regards.

-- 
Swâmi Petaramesh <swami@petaramesh.org> http://petaramesh.org PGP 9076E32E

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Re: Is there a "nossd" option ?

[Roman Mamedov]

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On Sun, 21 Jun 2015 19:13:10 +0200
Swâmi Petaramesh <swami@petaramesh.org> wrote:

> Hi,
> 
> Running a 3.19 Ubuntu kernel,
> 
> I'm currently budling a RAID-1 BTRFS set for which every underlying device is 
> a LUKS-encrypted device itself built out of a bcache device comprised of a 
> mechanical HD partition + an SSD cache partition.
> 
> Looks like it's working.
> 
> BUT I see that BTRFS decides by itself to mount with the "ssd" option as  
> bcache makes it think the device is not "rotational".
> 
> However I feel that a mechanical HD plus SSD bcache should probably not be 
> "SSD-optimized" as the underlying storage is indeed mechanical and bcache 
> already manages the SSD part optimization by itself - and I'm afraid the "SSD 
> optimization" could actually cause the mechanical storage to end up being much 
> more fragmented than it should...
> 
> So the question is : Is there a mount option such as "nossd" that I could use 
> to inhibit the automatic SSD "choice" that BTRFS makes ?

Yes the "nossd" option (written literally like that) does in fact exist.
It would have taken you less time to try if it works, than to write this
long-winded message. :)


-- 
With respect,
Roman

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Re: Is there a "nossd" option ?

[Swâmi Petaramesh]

Le dimanche 21 juin 2015 22:31:21 Roman Mamedov a écrit :
> 
> Yes the "nossd" option (written literally like that) does in fact exist.
> It would have taken you less time to try if it works, than to write this
> long-winded message. :)

Possibly. Unless trying a non-existing mount option causes the mount to fail, 
thus causing the system boot to fail, thus needing me to boot from a live 
rescue CD... that would take much longer than writing an half-page 
email ;-)

Best regards.


-- 
Swâmi Petaramesh <swami@petaramesh.org> http://petaramesh.org PGP 9076E32E

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Re: Is there a "nossd" option ?

[Eric Sandeen]

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> On Jun 21, 2015, at 1:11 PM, Swâmi Petaramesh <swami@petaramesh.org> wrote:
> 
> Le dimanche 21 juin 2015 22:31:21 Roman Mamedov a écrit :
>> 
>> Yes the "nossd" option (written literally like that) does in fact exist.
>> It would have taken you less time to try if it works, than to write this
>> long-winded message. :)
> 
> Possibly. Unless trying a non-existing mount option causes the mount to fail, 
> thus causing the system boot to fail, thus needing me to boot from a live 
> rescue CD... that would take much longer than writing an half-page 
> email ;-)
> 

Man pages work well too :)

http://manpages.ubuntu.com/manpages/utopic/man8/mount.8.html

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Re: Is there a "nossd" option ?

[Roman Mamedov]

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On Sun, 21 Jun 2015 20:11:25 +0200
Swâmi Petaramesh <swami@petaramesh.org> wrote:

> Le dimanche 21 juin 2015 22:31:21 Roman Mamedov a écrit :
> > 
> > Yes the "nossd" option (written literally like that) does in fact exist.
> > It would have taken you less time to try if it works, than to write this
> > long-winded message. :)
> 
> Possibly. Unless trying a non-existing mount option causes the mount to fail, 
> thus causing the system boot to fail, thus needing me to boot from a live 
> rescue CD... that would take much longer than writing an half-page 
> email ;-)
  
  mount / -o nossd,remount 

works too:

[3917300.257773] BTRFS info (device dm-0): not using ssd allocation scheme

As a side note, I used this option a lot in the past to make remote block
devices such as NBD or AoE not detect as SSDs.

-- 
With respect,
Roman

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