If you use NSFv4 you should be able to use locks and when a machine dies / fails to renew the lease, the other machine can take over.
On Friday, October 26, 2012, Todd Lipcon wrote: > NFS Locks typically last forever if you disconnect abruptly. So they are > not sufficient -- your standby wouldn't be able to take over without manual > intervention to remove the lock. > > If you want to build an unreliable system that might corrupt your data, > you could set up 'shell(/bin/true)' as a second fencing method. But, it's > really a bad idea. There are failure scenarios which could cause split > brain if you do this, and you'd very likely lose data. > > -Todd > > On Fri, Oct 26, 2012 at 1:59 AM, lei liu > <liulei...@gmail.com<javascript:_e({}, 'cvml', 'liulei...@gmail.com');> > > wrote: > >> We are using NFS for Shared storage, Can we use linux nfslcok service to >> implement IO Fencing ? >> >> >> 2012/10/26 Steve Loughran <ste...@hortonworks.com <javascript:_e({}, >> 'cvml', 'ste...@hortonworks.com');>> >> >>> >>> >>> On 25 October 2012 14:08, Todd Lipcon <t...@cloudera.com<javascript:_e({}, >>> 'cvml', 't...@cloudera.com');> >>> > wrote: >>> >>>> Hi Liu, >>>> >>>> Locks are not sufficient, because there is no way to enforce a lock in >>>> a distributed system without unbounded blocking. What you might be >>>> referring to is a lease, but leases are still problematic unless you can >>>> put bounds on the speed with which clocks progress on different machines, >>>> _and_ have strict guarantees on the way each node's scheduler works. With >>>> Linux and Java, the latter is tough. >>>> >>>> >>> on any OS running in any virtual environment, including EC2, time is >>> entirely unpredictable, just to make things worse. >>> >>> >>> On a single machine you can use file locking as the OS will know that >>> the process is dead and closes the file; other programs can attempt to open >>> the same file with exclusive locking -and, by getting the right failures, >>> know that something else has the file, hence the other process is live. >>> Shared NFS storage you need to mount with softlock set precisely to stop >>> file locks lasting until some lease has expired, because the on-host >>> liveness probes detect failure faster and want to react to it. >>> >>> >>> -Steve >>> >> >> > > > -- > Todd Lipcon > Software Engineer, Cloudera > -- Thanks -balaji -- http://balajin.net/blog/ http://flic.kr/balajijegan