Re: [PATCHES] new barriers - 2

Re: [PATCHES] new barriers - 2

[Tomasz Chmielewski]

> Here I announce 2nd version my new barrier support patches:
> http://people.redhat.com/mpatocka/patches/kernel/barriers/
> 
> They are against 2.6.29-rc3.
> 
> The most important enhancement is that with these patches, device mapper 
> is able to send barrier requests to lower devices.

I guess it still won't work for those using LVM on md (Linux software 
RAID) because md lacks barrier support? Do you know if someone is 
working on it?


-- 
Tomasz Chmielewski
http://wpkg.org

Re: [dm-devel] [PATCHES] new barriers - 2

[Mike Snitzer]

On Fri, Jan 30, 2009 at 5:15 AM, Tomasz Chmielewski <mangoo@wpkg.org> wrote:
>> Here I announce 2nd version my new barrier support patches:
>> http://people.redhat.com/mpatocka/patches/kernel/barriers/
>>
>> They are against 2.6.29-rc3.
>>
>> The most important enhancement is that with these patches, device mapper
>> is able to send barrier requests to lower devices.
>
> I guess it still won't work for those using LVM on md (Linux software RAID)
> because md lacks barrier support? Do you know if someone is working on it?

md raid1 has supported barriers since 2.6.17

But I'm not aware of any md work being done to support barriers in
other raid levels.  Judging by Neil Brown's thoughts on the matter
(from 2006) it would seem unlikely he is putting effort to it, please
see the following thread:
http://marc.info/?l=linux-raid&m=115321319003578&w=2
http://marc.info/?l=linux-raid&m=115335249503450&w=2

cc'ing linux-raid to see if others have more insight.

Re: [PATCHES] new barriers - 2

[Ric Wheeler]

Mike Snitzer wrote:
> On Fri, Jan 30, 2009 at 5:15 AM, Tomasz Chmielewski <mangoo@wpkg.org> wrote:
>   
>>> Here I announce 2nd version my new barrier support patches:
>>> http://people.redhat.com/mpatocka/patches/kernel/barriers/
>>>
>>> They are against 2.6.29-rc3.
>>>
>>> The most important enhancement is that with these patches, device mapper
>>> is able to send barrier requests to lower devices.
>>>       
>> I guess it still won't work for those using LVM on md (Linux software RAID)
>> because md lacks barrier support? Do you know if someone is working on it?
>>     
>
> md raid1 has supported barriers since 2.6.17
>
> But I'm not aware of any md work being done to support barriers in
> other raid levels.  Judging by Neil Brown's thoughts on the matter
> (from 2006) it would seem unlikely he is putting effort to it, please
> see the following thread:
> http://marc.info/?l=linux-raid&m=115321319003578&w=2
> http://marc.info/?l=linux-raid&m=115335249503450&w=2
>
> cc'ing linux-raid to see if others have more insight
>   

Neil, Hannes,

Is Mike's assumption above still true - no plans/thoughts about doing 
barrier support for RAID5/6 and so on?

At least some things (the null barrier op) are in place now since your 
summary of a couple years back, does this make it easier?

Thanks!

Ric

[PATCHES] new barriers - 2

[Mikulas Patocka]

Hi

Here I announce 2nd version my new barrier support patches:
http://people.redhat.com/mpatocka/patches/kernel/barriers/

They are against 2.6.29-rc3.

The most important enhancement is that with these patches, device mapper 
is able to send barrier requests to lower devices.

So it should be safe to enable write cache with hdparm -W 1 command on 
disks used in lvm and get enhanced performance because of write caching.

(prior to this patch, if you enabled write cache, you'd get misordered 
writes if you used journaling filesystems, because the barriers wouldn't 
get through to the real devices).

The barriers should work on linear volumes, mirrors, snapshots and 
multipath volumes. On mirrors and multipath, cache flush errors are 
ignored (this may be further improved).

Mikulas