readonly start of Linux RAID

readonly start of Linux RAID

[David Chow]

Hi Neil,

I've been reading some archives in the Linux RAID mailing list. Someone ask for implementing a readonly mode instead of degraded mode in RAID-1/5 setups. I'm falling into a similar problem . I think it is important to have a readonly mode on starting a RAID device or operating on a RAID device. Think of systems that didn't want to rebuild their RAID immediately after an unclean shutdown... Calling autorun() ioctls will make all devices starting rebuild themselves in case of any available disk exists. In case we are on a shared storage system, the active cluster might have using the RAID disks which seems to be unclean on the other standby cluster. The standby cluster might want to have a read-only inspection of the shared storage. In case of a high availability cluster system failover, the standby cluster might want to determine to start full read/write access by some tools instead of forced automatic at system boot (initrd calling raidautorun). In such circumstances, the cur
 rent md driver cannot be used. This also prohibits many implementation of a high availability system from implement linux RAID on a shared storage on an HA system which is extremely important. I guess, this problem also comes with LVM and other similar volume management system. I'm currently studying the md.c code in a 2.4.19 kernel which I see implementing a read-only mode for md is possible. Please give advice or anything happening, so that I don't spend duplicated efforts. Thanks.


regards,
David Chow

Re: readonly start of Linux RAID

[Steven Dake]

David,

Read this regarding enhancing the MD driver to work in a shared storage 
environment.

http://marc.theaimsgroup.com/?l=linux-raid&m=104170749423143&w=2

David Chow wrote:

>Hi Neil,
>
>I've been reading some archives in the Linux RAID mailing list. Someone ask for implementing a readonly mode instead of degraded mode in RAID-1/5 setups. I'm falling into a similar problem . I think it is important to have a readonly mode on starting a RAID device or operating on a RAID device. Think of systems that didn't want to rebuild their RAID immediately after an unclean shutdown... Calling autorun() ioctls will make all devices starting rebuild themselves in case of any available disk exists. In case we are on a shared storage system, the active cluster might have using the RAID disks which seems to be unclean on the other standby cluster. The standby cluster might want to have a read-only inspection of the shared storage. In case of a high availability cluster system failover, the standby cluster might want to determine to start full read/write access by some tools instead of forced automatic at system boot (initrd calling raidautorun). In such circumstances, the cu
 rr!
>!
>ent md driver cannot be used. This also prohibits many implementation of a high availability system from implement linux RAID on a shared storage on an HA system which is extremely important. I guess, this problem also comes with LVM and other similar volume management system. I'm currently studying the md.c code in a 2.4.19 kernel which I see implementing a read-only mode for md is possible. Please give advice or anything happening, so that I don't spend duplicated efforts. Thanks.
>
>
>regards,
>David Chow
>
>
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>  
>

Re: readonly start of Linux RAID

[David Chow]

Steve,

Thanks for replying.  The message you given talked about a cluster 
implemetation of MD driver which is completely out of the scope of linux 
raid. I do think such implementation belongs to some cluster file system 
or volume management systems, and it seems such implementation of md 
will be very hard to get into the stock kernel . What I am asking is a 
generic simple enhancement of the md which might be useful in lot of 
areas (shared storage is just one example), and even administration on 
preventing some md being rebuild immediate after an unclean shutdown or 
similar senarios. The work to do is mimimal comparing the work on a 
cluster md driver implementation.

Someone talk about this...
http://marc.theaimsgroup.com/?l=linux-raid&m=103300356601897&w=2

Neil talked about this before too...
http://marc.theaimsgroup.com/?l=linux-raid&m=102669565104333&w=2

Please give pointer to access information so that I can keep track the 
read-only stuff if it exists. Thanks.

regards,
David

Steven Dake wrote:

> David,
>
> Read this regarding enhancing the MD driver to work in a shared 
> storage environment.
>
> http://marc.theaimsgroup.com/?l=linux-raid&m=104170749423143&w=2
>
> David Chow wrote:
>
>> Hi Neil,
>>
>> I've been reading some archives in the Linux RAID mailing list. 
>> Someone ask for implementing a readonly mode instead of degraded mode 
>> in RAID-1/5 setups. I'm falling into a similar problem . I think it 
>> is important to have a readonly mode on starting a RAID device or 
>> operating on a RAID device. Think of systems that didn't want to 
>> rebuild their RAID immediately after an unclean shutdown... Calling 
>> autorun() ioctls will make all devices starting rebuild themselves in 
>> case of any available disk exists. In case we are on a shared storage 
>> system, the active cluster might have using the RAID disks which 
>> seems to be unclean on the other standby cluster. The standby cluster 
>> might want to have a read-only inspection of the shared storage. In 
>> case of a high availability cluster system failover, the standby 
>> cluster might want to determine to start full read/write access by 
>> some tools instead of forced automatic at system boot (initrd calling 
>> raidautorun). In such circumstances, the curr!
>> !
>> ent md driver cannot be used. This also prohibits many implementation 
>> of a high availability system from implement linux RAID on a shared 
>> storage on an HA system which is extremely important. I guess, this 
>> problem also comes with LVM and other similar volume management 
>> system. I'm currently studying the md.c code in a 2.4.19 kernel which 
>> I see implementing a read-only mode for md is possible. Please give 
>> advice or anything happening, so that I don't spend duplicated 
>> efforts. Thanks.
>>
>>
>> regards,
>> David Chow
>>
>>

Re: readonly start of Linux RAID

[Steven Dake]

David,

The changes to the md driver itself are minimal to support clustering 
and I think they are likely to make kernel.org (the ability to set 
read-only or write mode with some extensions to support resyncs between 
cluster nodes).  The significant changes are to the userland utilities.

I also have an implementation of raid multihost locking, which locks a 
RAID array to a specific host ID (based upon geographical address, 
fibrechannel host's wwn, or scsi host id).  This ensures that a RAID 
cannot be shared between hosts and will prevent other hosts from 
starting the raid or causing any problems with it.

Regards,
-steve

David Chow wrote:

> Steve,
>
> Thanks for replying.  The message you given talked about a cluster 
> implemetation of MD driver which is completely out of the scope of 
> linux raid. I do think such implementation belongs to some cluster 
> file system or volume management systems, and it seems such 
> implementation of md will be very hard to get into the stock kernel . 
> What I am asking is a generic simple enhancement of the md which might 
> be useful in lot of areas (shared storage is just one example), and 
> even administration on preventing some md being rebuild immediate 
> after an unclean shutdown or similar senarios. The work to do is 
> mimimal comparing the work on a cluster md driver implementation.
>
> Someone talk about this...
> http://marc.theaimsgroup.com/?l=linux-raid&m=103300356601897&w=2
>
> Neil talked about this before too...
> http://marc.theaimsgroup.com/?l=linux-raid&m=102669565104333&w=2
>
> Please give pointer to access information so that I can keep track the 
> read-only stuff if it exists. Thanks.
>
> regards,
> David
>
> Steven Dake wrote:
>
>> David,
>>
>> Read this regarding enhancing the MD driver to work in a shared 
>> storage environment.
>>
>> http://marc.theaimsgroup.com/?l=linux-raid&m=104170749423143&w=2
>>
>> David Chow wrote:
>>
>>> Hi Neil,
>>>
>>> I've been reading some archives in the Linux RAID mailing list. 
>>> Someone ask for implementing a readonly mode instead of degraded 
>>> mode in RAID-1/5 setups. I'm falling into a similar problem . I 
>>> think it is important to have a readonly mode on starting a RAID 
>>> device or operating on a RAID device. Think of systems that didn't 
>>> want to rebuild their RAID immediately after an unclean shutdown... 
>>> Calling autorun() ioctls will make all devices starting rebuild 
>>> themselves in case of any available disk exists. In case we are on a 
>>> shared storage system, the active cluster might have using the RAID 
>>> disks which seems to be unclean on the other standby cluster. The 
>>> standby cluster might want to have a read-only inspection of the 
>>> shared storage. In case of a high availability cluster system 
>>> failover, the standby cluster might want to determine to start full 
>>> read/write access by some tools instead of forced automatic at 
>>> system boot (initrd calling raidautorun). In such circumstances, the 
>>> curr!
>>> !
>>> ent md driver cannot be used. This also prohibits many 
>>> implementation of a high availability system from implement linux 
>>> RAID on a shared storage on an HA system which is extremely 
>>> important. I guess, this problem also comes with LVM and other 
>>> similar volume management system. I'm currently studying the md.c 
>>> code in a 2.4.19 kernel which I see implementing a read-only mode 
>>> for md is possible. Please give advice or anything happening, so 
>>> that I don't spend duplicated efforts. Thanks.
>>>
>>>
>>> regards,
>>> David Chow
>>>
>>>
>
>
>