Re: [ceph-users] Write back cache removal

2017-01-12 Thread Wido den Hollander 

> Op 10 januari 2017 om 22:05 schreef Nick Fisk <n...@fisk.me.uk>:
> 
> 
> From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of 
> Stuart Harland
> Sent: 10 January 2017 11:58
> To: Wido den Hollander <w...@42on.com>
> Cc: ceph new <ceph-users@lists.ceph.com>; n...@fisk.me.uk
> Subject: Re: [ceph-users] Write back cache removal
> 
>  
> 
> Yes Wido, you are correct. There is a RBD pool in the cluster, but is not 
> currently running with a cache attached. The Pool I’m trying to manage here 
> is only used by Librados to write objects directly to the pool as opposed to 
> any of the other niceties that ceph provides.
> 
>  
> 
> Specifically I ran:
> 
>  
> 
> `ceph osd tier cache-mode  forward`
> 
>  
> 
> which returned `Error EPERM: 'forward' is not a well-supported cache mode and 
> may corrupt your data.  pass --yes-i-really-mean-it to force.`
> 
>  
> 
> Currently we are running 10.2.5. I suspect that it’s fine in our use case, 
> however given the sparsity of the documentation I didn’t like to assume 
> anything.
> 
>  
> 
>  
> 
> Regards
> 
>  
> 
> Stuart
> 
>  
> 
>  
> 
> Yep, sorry, I got this post mixed up with the one from Daznis yesterday who 
> was using RBD’s. I think that warning was introduced as some bugs were found 
> that corrupted some users data after frequently switching between writeback 
> and forward modes. As it is very rarely used mode and so wasn’t worth the 
> testing I believe the decision was taken to just implement the warning. If 
> you are using it as part of removing a cache tier and you have already 
> flushed the tier, then I believe it should be fine to use. 
> 
>  

I suggest that you stop writes if possible so that nothing changes.

Then drain the cache and set the mode to forward.

Wido

> 
> Another way would probably be to set the min promote thresholds to higher 
> than your hit set counts, this will abuse the tiering logic but should also 
> stop anything getting promoted into your cache tier.
> 
>  
> 
>  
> 
>  
> 
>  
> 
> On 10 Jan 2017, at 09:52, Wido den Hollander <w...@42on.com 
> <mailto:w...@42on.com> > wrote:
> 
>  
> 
> 
> Op 10 januari 2017 om 9:52 schreef Nick Fisk <n...@fisk.me.uk 
> <mailto:n...@fisk.me.uk> >:
> 
> 
> 
> 
> 
> -Original Message-
> From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of Wido 
> den Hollander
> Sent: 10 January 2017 07:54
> To: ceph new <ceph-users@lists.ceph.com <mailto:ceph-users@lists.ceph.com> >; 
> Stuart Harland <s.harl...@livelinktechnology.net 
> <mailto:s.harl...@livelinktechnology.net> >
> Subject: Re: [ceph-users] Write back cache removal
> 
> 
> 
> 
> 
> Op 9 januari 2017 om 13:02 schreef Stuart Harland 
> <s.harl...@livelinktechnology.net <mailto:s.harl...@livelinktechnology.net> >:
> 
> 
> Hi,
> 
> We’ve been operating a ceph storage system storing files using librados 
> (using a replicated pool on rust disks). We implemented a
> 
> cache over the top of this with SSDs, however we now want to turn this off.
> 
> 
> 
> 
> The documentation suggests setting the cache mode to forward before draining 
> the pool, however the ceph management
> 
> controller spits out an error about this saying that it is unsupported and 
> hence dangerous.
> 
> 
> 
>  
> 
> 
> What version of Ceph are you running?
> 
> And can you paste the exact command and the output?
> 
> Wido
> 
> 
> Hi Wido,
> 
> I think this has been discussed before and looks like it might be a current 
> limitation. Not sure if it's on anybody's radar to fix.
> 
> https://www.mail-archive.com/ceph-users@lists.ceph.com/msg24472.html
> 
> 
> Might be, but afaik they are using their own application which writes to 
> RADOS using librados, not RBD.
> 
> Is that correct Stuart?
> 
> Wido
> 
> 
> 
> 
> Nick
> 
> 
> 
> 
> 
> 
> 
> 
> The thing is I cannot really locate any documentation as to why it’s 
> considered unsupported and under what conditions it is expected
> 
> to fail: I have read a passing comment about EC pools having data corruption, 
> but we are using replicated pools.
> 
> 
> 
> 
> Is this something that is safe to do?
> 
> Otherwise I have noted the read proxy mode of cache tiers which is documented 
> as a mechanism to transition from write back to
> 
> disabled, however the documentation is even sparser on this than forward 
> mode. Would this be a better approach if there is some
> unsupporte

Re: [ceph-users] Write back cache removal

2017-01-10 Thread Nick Fisk 
From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of Stuart 
Harland
Sent: 10 January 2017 11:58
To: Wido den Hollander <w...@42on.com>
Cc: ceph new <ceph-users@lists.ceph.com>; n...@fisk.me.uk
Subject: Re: [ceph-users] Write back cache removal

 

Yes Wido, you are correct. There is a RBD pool in the cluster, but is not 
currently running with a cache attached. The Pool I’m trying to manage here is 
only used by Librados to write objects directly to the pool as opposed to any 
of the other niceties that ceph provides.

 

Specifically I ran:

 

`ceph osd tier cache-mode  forward`

 

which returned `Error EPERM: 'forward' is not a well-supported cache mode and 
may corrupt your data.  pass --yes-i-really-mean-it to force.`

 

Currently we are running 10.2.5. I suspect that it’s fine in our use case, 
however given the sparsity of the documentation I didn’t like to assume 
anything.

 

 

Regards

 

Stuart

 

 

Yep, sorry, I got this post mixed up with the one from Daznis yesterday who was 
using RBD’s. I think that warning was introduced as some bugs were found that 
corrupted some users data after frequently switching between writeback and 
forward modes. As it is very rarely used mode and so wasn’t worth the testing I 
believe the decision was taken to just implement the warning. If you are using 
it as part of removing a cache tier and you have already flushed the tier, then 
I believe it should be fine to use. 

 

Another way would probably be to set the min promote thresholds to higher than 
your hit set counts, this will abuse the tiering logic but should also stop 
anything getting promoted into your cache tier.

 

 

 

 

On 10 Jan 2017, at 09:52, Wido den Hollander <w...@42on.com 
<mailto:w...@42on.com> > wrote:

 


Op 10 januari 2017 om 9:52 schreef Nick Fisk <n...@fisk.me.uk 
<mailto:n...@fisk.me.uk> >:





-Original Message-
From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of Wido 
den Hollander
Sent: 10 January 2017 07:54
To: ceph new <ceph-users@lists.ceph.com <mailto:ceph-users@lists.ceph.com> >; 
Stuart Harland <s.harl...@livelinktechnology.net 
<mailto:s.harl...@livelinktechnology.net> >
Subject: Re: [ceph-users] Write back cache removal





Op 9 januari 2017 om 13:02 schreef Stuart Harland 
<s.harl...@livelinktechnology.net <mailto:s.harl...@livelinktechnology.net> >:


Hi,

We’ve been operating a ceph storage system storing files using librados (using 
a replicated pool on rust disks). We implemented a

cache over the top of this with SSDs, however we now want to turn this off.




The documentation suggests setting the cache mode to forward before draining 
the pool, however the ceph management

controller spits out an error about this saying that it is unsupported and 
hence dangerous.



 


What version of Ceph are you running?

And can you paste the exact command and the output?

Wido


Hi Wido,

I think this has been discussed before and looks like it might be a current 
limitation. Not sure if it's on anybody's radar to fix.

https://www.mail-archive.com/ceph-users@lists.ceph.com/msg24472.html


Might be, but afaik they are using their own application which writes to RADOS 
using librados, not RBD.

Is that correct Stuart?

Wido




Nick








The thing is I cannot really locate any documentation as to why it’s considered 
unsupported and under what conditions it is expected

to fail: I have read a passing comment about EC pools having data corruption, 
but we are using replicated pools.




Is this something that is safe to do?

Otherwise I have noted the read proxy mode of cache tiers which is documented 
as a mechanism to transition from write back to

disabled, however the documentation is even sparser on this than forward mode. 
Would this be a better approach if there is some
unsupported behaviour in the forward mode cache option?




Any thoughts would be appreciated - we really cannot afford to corrupt the 
data, and I really do not want to have to do some

manual software based eviction on this data.




regards

Stuart


− Stuart Harland:
Infrastructure Engineer
Email: s.harl...@livelinktechnology.net 
<mailto:s.harl...@livelinktechnology.net>  
<mailto:s.harl...@livelinktechnology.net>



LiveLink Technology Ltd
McCormack House
56A East Street
Havant
PO9 1BS

IMPORTANT: The information transmitted in this e-mail is intended only for the 
person or entity to whom it is addressed and may

contain confidential and/or privileged information. If you are not the intended 
recipient of this message, please do not read, copy, use
or disclose this communication and notify the sender immediately. Any review, 
retransmission, dissemination or other use of, or
taking any action in reliance upon this information by persons or entities 
other than the intended recipient is prohibited. Any views or
opinions presented in this e-mail are so

Re: [ceph-users] Write back cache removal

2017-01-10 Thread Stuart Harland 
Yes Wido, you are correct. There is a RBD pool in the cluster, but is not 
currently running with a cache attached. The Pool I’m trying to manage here is 
only used by Librados to write objects directly to the pool as opposed to any 
of the other niceties that ceph provides.

Specifically I ran:

`ceph osd tier cache-mode  forward`

which returned `Error EPERM: 'forward' is not a well-supported cache mode and 
may corrupt your data.  pass --yes-i-really-mean-it to force.`

Currently we are running 10.2.5. I suspect that it’s fine in our use case, 
however given the sparsity of the documentation I didn’t like to assume 
anything.


Regards

Stuart





> On 10 Jan 2017, at 09:52, Wido den Hollander <w...@42on.com> wrote:
> 
>> 
>> Op 10 januari 2017 om 9:52 schreef Nick Fisk <n...@fisk.me.uk 
>> <mailto:n...@fisk.me.uk>>:
>> 
>> 
>>> -Original Message-
>>> From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of 
>>> Wido den Hollander
>>> Sent: 10 January 2017 07:54
>>> To: ceph new <ceph-users@lists.ceph.com>; Stuart Harland 
>>> <s.harl...@livelinktechnology.net>
>>> Subject: Re: [ceph-users] Write back cache removal
>>> 
>>> 
>>>> Op 9 januari 2017 om 13:02 schreef Stuart Harland 
>>>> <s.harl...@livelinktechnology.net>:
>>>> 
>>>> 
>>>> Hi,
>>>> 
>>>> We’ve been operating a ceph storage system storing files using librados 
>>>> (using a replicated pool on rust disks). We implemented a
>>> cache over the top of this with SSDs, however we now want to turn this off.
>>>> 
>>>> The documentation suggests setting the cache mode to forward before 
>>>> draining the pool, however the ceph management
>>> controller spits out an error about this saying that it is unsupported and 
>>> hence dangerous.
>>>> 
>>> 
>>> What version of Ceph are you running?
>>> 
>>> And can you paste the exact command and the output?
>>> 
>>> Wido
>> 
>> Hi Wido,
>> 
>> I think this has been discussed before and looks like it might be a current 
>> limitation. Not sure if it's on anybody's radar to fix.
>> 
>> https://www.mail-archive.com/ceph-users@lists.ceph.com/msg24472.html 
>> <https://www.mail-archive.com/ceph-users@lists.ceph.com/msg24472.html>
>> 
> 
> Might be, but afaik they are using their own application which writes to 
> RADOS using librados, not RBD.
> 
> Is that correct Stuart?
> 
> Wido
> 
>> Nick
>> 
>>> 
>>>> The thing is I cannot really locate any documentation as to why it’s 
>>>> considered unsupported and under what conditions it is expected
>>> to fail: I have read a passing comment about EC pools having data 
>>> corruption, but we are using replicated pools.
>>>> 
>>>> Is this something that is safe to do?
>>>> 
>>>> Otherwise I have noted the read proxy mode of cache tiers which is 
>>>> documented as a mechanism to transition from write back to
>>> disabled, however the documentation is even sparser on this than forward 
>>> mode. Would this be a better approach if there is some
>>> unsupported behaviour in the forward mode cache option?
>>>> 
>>>> Any thoughts would be appreciated - we really cannot afford to corrupt the 
>>>> data, and I really do not want to have to do some
>>> manual software based eviction on this data.
>>>> 
>>>> regards
>>>> 
>>>> Stuart
>>>> 
>>>> 
>>>> − Stuart Harland:
>>>> Infrastructure Engineer
>>>> Email: s.harl...@livelinktechnology.net 
>>>> <mailto:s.harl...@livelinktechnology.net>
>>>> 
>>>> 
>>>> 
>>>> LiveLink Technology Ltd
>>>> McCormack House
>>>> 56A East Street
>>>> Havant
>>>> PO9 1BS
>>>> 
>>>> IMPORTANT: The information transmitted in this e-mail is intended only for 
>>>> the person or entity to whom it is addressed and may
>>> contain confidential and/or privileged information. If you are not the 
>>> intended recipient of this message, please do not read, copy, use
>>> or disclose this communication and notify the sender immediately. Any 
>>> review, retransmission, dissemination or other use of, or
>>> taking any action in reliance upon this information by persons or entities 
>>

Re: [ceph-users] Write back cache removal

2017-01-10 Thread jiajia zhong 
It's fixed since v0.94.6, http://ceph.com/releases/v0-94-6-hammer-released/


   - fs: CephFS restriction on removing cache tiers is overly strict (
   issue#11504 <http://tracker.ceph.com/issues/11504>, pr#6402
   <http://github.com/ceph/ceph/pull/6402>, John Spray)


but you have to make sure your release patched.

2017-01-10 16:52 GMT+08:00 Nick Fisk <n...@fisk.me.uk>:

> > -Original Message-
> > From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf
> Of Wido den Hollander
> > Sent: 10 January 2017 07:54
> > To: ceph new <ceph-users@lists.ceph.com>; Stuart Harland <
> s.harl...@livelinktechnology.net>
> > Subject: Re: [ceph-users] Write back cache removal
> >
> >
> > > Op 9 januari 2017 om 13:02 schreef Stuart Harland <
> s.harl...@livelinktechnology.net>:
> > >
> > >
> > > Hi,
> > >
> > > We’ve been operating a ceph storage system storing files using
> librados (using a replicated pool on rust disks). We implemented a
> > cache over the top of this with SSDs, however we now want to turn this
> off.
> > >
> > > The documentation suggests setting the cache mode to forward before
> draining the pool, however the ceph management
> > controller spits out an error about this saying that it is unsupported
> and hence dangerous.
> > >
> >
> > What version of Ceph are you running?
> >
> > And can you paste the exact command and the output?
> >
> > Wido
>
> Hi Wido,
>
> I think this has been discussed before and looks like it might be a
> current limitation. Not sure if it's on anybody's radar to fix.
>
> https://www.mail-archive.com/ceph-users@lists.ceph.com/msg24472.html
>
> Nick
>
> >
> > > The thing is I cannot really locate any documentation as to why it’s
> considered unsupported and under what conditions it is expected
> > to fail: I have read a passing comment about EC pools having data
> corruption, but we are using replicated pools.
> > >
> > > Is this something that is safe to do?
> > >
> > > Otherwise I have noted the read proxy mode of cache tiers which is
> documented as a mechanism to transition from write back to
> > disabled, however the documentation is even sparser on this than forward
> mode. Would this be a better approach if there is some
> > unsupported behaviour in the forward mode cache option?
> > >
> > > Any thoughts would be appreciated - we really cannot afford to corrupt
> the data, and I really do not want to have to do some
> > manual software based eviction on this data.
> > >
> > > regards
> > >
> > > Stuart
> > >
> > >
> > >  − Stuart Harland:
> > > Infrastructure Engineer
> > > Email: s.harl...@livelinktechnology.net <mailto:s.harland@
> livelinktechnology.net>
> > >
> > >
> > >
> > > LiveLink Technology Ltd
> > > McCormack House
> > > 56A East Street
> > > Havant
> > > PO9 1BS
> > >
> > > IMPORTANT: The information transmitted in this e-mail is intended only
> for the person or entity to whom it is addressed and may
> > contain confidential and/or privileged information. If you are not the
> intended recipient of this message, please do not read, copy, use
> > or disclose this communication and notify the sender immediately. Any
> review, retransmission, dissemination or other use of, or
> > taking any action in reliance upon this information by persons or
> entities other than the intended recipient is prohibited. Any views or
> > opinions presented in this e-mail are solely those of the author and do
> not necessarily represent those of LiveLink. This e-mail
> > message has been checked for the presence of computer viruses. However,
> LiveLink is not able to accept liability for any damage
> > caused by this e-mail.
> > >
> > >
> > >
> > > ___
> > > ceph-users mailing list
> > > ceph-users@lists.ceph.com
> > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> > ___
> > ceph-users mailing list
> > ceph-users@lists.ceph.com
> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
>
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Re: [ceph-users] Write back cache removal

2017-01-10 Thread Wido den Hollander 

> Op 10 januari 2017 om 9:52 schreef Nick Fisk <n...@fisk.me.uk>:
> 
> 
> > -Original Message-
> > From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of 
> > Wido den Hollander
> > Sent: 10 January 2017 07:54
> > To: ceph new <ceph-users@lists.ceph.com>; Stuart Harland 
> > <s.harl...@livelinktechnology.net>
> > Subject: Re: [ceph-users] Write back cache removal
> > 
> > 
> > > Op 9 januari 2017 om 13:02 schreef Stuart Harland 
> > > <s.harl...@livelinktechnology.net>:
> > >
> > >
> > > Hi,
> > >
> > > We’ve been operating a ceph storage system storing files using librados 
> > > (using a replicated pool on rust disks). We implemented a
> > cache over the top of this with SSDs, however we now want to turn this off.
> > >
> > > The documentation suggests setting the cache mode to forward before 
> > > draining the pool, however the ceph management
> > controller spits out an error about this saying that it is unsupported and 
> > hence dangerous.
> > >
> > 
> > What version of Ceph are you running?
> > 
> > And can you paste the exact command and the output?
> > 
> > Wido
> 
> Hi Wido,
> 
> I think this has been discussed before and looks like it might be a current 
> limitation. Not sure if it's on anybody's radar to fix.
> 
> https://www.mail-archive.com/ceph-users@lists.ceph.com/msg24472.html
> 

Might be, but afaik they are using their own application which writes to RADOS 
using librados, not RBD.

Is that correct Stuart?

Wido

> Nick
> 
> > 
> > > The thing is I cannot really locate any documentation as to why it’s 
> > > considered unsupported and under what conditions it is expected
> > to fail: I have read a passing comment about EC pools having data 
> > corruption, but we are using replicated pools.
> > >
> > > Is this something that is safe to do?
> > >
> > > Otherwise I have noted the read proxy mode of cache tiers which is 
> > > documented as a mechanism to transition from write back to
> > disabled, however the documentation is even sparser on this than forward 
> > mode. Would this be a better approach if there is some
> > unsupported behaviour in the forward mode cache option?
> > >
> > > Any thoughts would be appreciated - we really cannot afford to corrupt 
> > > the data, and I really do not want to have to do some
> > manual software based eviction on this data.
> > >
> > > regards
> > >
> > > Stuart
> > >
> > >
> > >  − Stuart Harland:
> > > Infrastructure Engineer
> > > Email: s.harl...@livelinktechnology.net 
> > > <mailto:s.harl...@livelinktechnology.net>
> > >
> > >
> > >
> > > LiveLink Technology Ltd
> > > McCormack House
> > > 56A East Street
> > > Havant
> > > PO9 1BS
> > >
> > > IMPORTANT: The information transmitted in this e-mail is intended only 
> > > for the person or entity to whom it is addressed and may
> > contain confidential and/or privileged information. If you are not the 
> > intended recipient of this message, please do not read, copy, use
> > or disclose this communication and notify the sender immediately. Any 
> > review, retransmission, dissemination or other use of, or
> > taking any action in reliance upon this information by persons or entities 
> > other than the intended recipient is prohibited. Any views or
> > opinions presented in this e-mail are solely those of the author and do not 
> > necessarily represent those of LiveLink. This e-mail
> > message has been checked for the presence of computer viruses. However, 
> > LiveLink is not able to accept liability for any damage
> > caused by this e-mail.
> > >
> > >
> > >
> > > ___
> > > ceph-users mailing list
> > > ceph-users@lists.ceph.com
> > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> > ___
> > ceph-users mailing list
> > ceph-users@lists.ceph.com
> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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Re: [ceph-users] Write back cache removal

2017-01-10 Thread Nick Fisk 
> -Original Message-
> From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of Wido 
> den Hollander
> Sent: 10 January 2017 07:54
> To: ceph new <ceph-users@lists.ceph.com>; Stuart Harland 
> <s.harl...@livelinktechnology.net>
> Subject: Re: [ceph-users] Write back cache removal
> 
> 
> > Op 9 januari 2017 om 13:02 schreef Stuart Harland 
> > <s.harl...@livelinktechnology.net>:
> >
> >
> > Hi,
> >
> > We’ve been operating a ceph storage system storing files using librados 
> > (using a replicated pool on rust disks). We implemented a
> cache over the top of this with SSDs, however we now want to turn this off.
> >
> > The documentation suggests setting the cache mode to forward before 
> > draining the pool, however the ceph management
> controller spits out an error about this saying that it is unsupported and 
> hence dangerous.
> >
> 
> What version of Ceph are you running?
> 
> And can you paste the exact command and the output?
> 
> Wido

Hi Wido,

I think this has been discussed before and looks like it might be a current 
limitation. Not sure if it's on anybody's radar to fix.

https://www.mail-archive.com/ceph-users@lists.ceph.com/msg24472.html

Nick

> 
> > The thing is I cannot really locate any documentation as to why it’s 
> > considered unsupported and under what conditions it is expected
> to fail: I have read a passing comment about EC pools having data corruption, 
> but we are using replicated pools.
> >
> > Is this something that is safe to do?
> >
> > Otherwise I have noted the read proxy mode of cache tiers which is 
> > documented as a mechanism to transition from write back to
> disabled, however the documentation is even sparser on this than forward 
> mode. Would this be a better approach if there is some
> unsupported behaviour in the forward mode cache option?
> >
> > Any thoughts would be appreciated - we really cannot afford to corrupt the 
> > data, and I really do not want to have to do some
> manual software based eviction on this data.
> >
> > regards
> >
> > Stuart
> >
> >
> >  − Stuart Harland:
> > Infrastructure Engineer
> > Email: s.harl...@livelinktechnology.net 
> > <mailto:s.harl...@livelinktechnology.net>
> >
> >
> >
> > LiveLink Technology Ltd
> > McCormack House
> > 56A East Street
> > Havant
> > PO9 1BS
> >
> > IMPORTANT: The information transmitted in this e-mail is intended only for 
> > the person or entity to whom it is addressed and may
> contain confidential and/or privileged information. If you are not the 
> intended recipient of this message, please do not read, copy, use
> or disclose this communication and notify the sender immediately. Any review, 
> retransmission, dissemination or other use of, or
> taking any action in reliance upon this information by persons or entities 
> other than the intended recipient is prohibited. Any views or
> opinions presented in this e-mail are solely those of the author and do not 
> necessarily represent those of LiveLink. This e-mail
> message has been checked for the presence of computer viruses. However, 
> LiveLink is not able to accept liability for any damage
> caused by this e-mail.
> >
> >
> >
> > ___
> > ceph-users mailing list
> > ceph-users@lists.ceph.com
> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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Re: [ceph-users] Write back cache removal

2017-01-09 Thread Wido den Hollander 

> Op 9 januari 2017 om 13:02 schreef Stuart Harland 
> :
> 
> 
> Hi,
> 
> We’ve been operating a ceph storage system storing files using librados 
> (using a replicated pool on rust disks). We implemented a cache over the top 
> of this with SSDs, however we now want to turn this off.
> 
> The documentation suggests setting the cache mode to forward before draining 
> the pool, however the ceph management controller spits out an error about 
> this saying that it is unsupported and hence dangerous.
> 

What version of Ceph are you running?

And can you paste the exact command and the output?

Wido

> The thing is I cannot really locate any documentation as to why it’s 
> considered unsupported and under what conditions it is expected to fail: I 
> have read a passing comment about EC pools having data corruption, but we are 
> using replicated pools.
> 
> Is this something that is safe to do?
> 
> Otherwise I have noted the read proxy mode of cache tiers which is documented 
> as a mechanism to transition from write back to disabled, however the 
> documentation is even sparser on this than forward mode. Would this be a 
> better approach if there is some unsupported behaviour in the forward mode 
> cache option? 
> 
> Any thoughts would be appreciated - we really cannot afford to corrupt the 
> data, and I really do not want to have to do some manual software based 
> eviction on this data.
> 
> regards
> 
> Stuart
> 
> 
>  − Stuart Harland: 
> Infrastructure Engineer
> Email: s.harl...@livelinktechnology.net 
> 
> 
> 
> 
> LiveLink Technology Ltd
> McCormack House
> 56A East Street
> Havant
> PO9 1BS
> 
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[ceph-users] Write back cache removal

2017-01-09 Thread Stuart Harland 
Hi,

We’ve been operating a ceph storage system storing files using librados (using 
a replicated pool on rust disks). We implemented a cache over the top of this 
with SSDs, however we now want to turn this off.

The documentation suggests setting the cache mode to forward before draining 
the pool, however the ceph management controller spits out an error about this 
saying that it is unsupported and hence dangerous.

The thing is I cannot really locate any documentation as to why it’s considered 
unsupported and under what conditions it is expected to fail: I have read a 
passing comment about EC pools having data corruption, but we are using 
replicated pools.

Is this something that is safe to do?

Otherwise I have noted the read proxy mode of cache tiers which is documented 
as a mechanism to transition from write back to disabled, however the 
documentation is even sparser on this than forward mode. Would this be a better 
approach if there is some unsupported behaviour in the forward mode cache 
option? 

Any thoughts would be appreciated - we really cannot afford to corrupt the 
data, and I really do not want to have to do some manual software based 
eviction on this data.

regards

Stuart


 − Stuart Harland: 
Infrastructure Engineer
Email: s.harl...@livelinktechnology.net 




LiveLink Technology Ltd
McCormack House
56A East Street
Havant
PO9 1BS

IMPORTANT: The information transmitted in this e-mail is intended only for the 
person or entity to whom it is addressed and may contain confidential and/or 
privileged information. If you are not the intended recipient of this message, 
please do not read, copy, use or disclose this communication and notify the 
sender immediately. Any review, retransmission, dissemination or other use of, 
or taking any action in reliance upon this information by persons or entities 
other than the intended recipient is prohibited. Any views or opinions 
presented in this e-mail are solely those of the author and do not necessarily 
represent those of LiveLink. This e-mail message has been checked for the 
presence of computer viruses. However, LiveLink is not able to accept liability 
for any damage caused by this e-mail.



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