readonly start of Linux RAID
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
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
Quoted 3 lines · 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 cu
rr!
Quoted 17 lines
!
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 themd.ccode 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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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
Quoted 19 lines · 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
Quoted 11 lines · 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 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 themd.ccode 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
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
Quoted 39 lines · 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=2Neil talked about this before too...
http://marc.theaimsgroup.com/?l=linux-raid&m=102669565104333&w=2Please give pointer to access information so that I can keep track the read-only stuff if it exists. Thanks.
regards,
DavidQuoted 19 lines · 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
Quoted 11 lines · 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 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 themd.ccode 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