[Lustre-discuss] Newbie question: File locking, synchronicity, order, and ownership

[Nochum Klein]

Hi Atul,

Thanks a lot -- this is very helpful!

So assuming the application is performing the following fcntl() call to set
a file segment lock:

    struct flock fl;
    int err;

    fl.l_type = F_WRLCK;
    fl.l_whence = 0;
    fl.l_start = 0;
    fl.l_len = 0;    /* len = 0 means until end of file */

    err = fcntl(file, F_SETLK, &fl);

I should be able to achieve the desired behavior if I enable cluster-wide
locking with the /-o flock/ mount option.  Is this correct?

Thanks again!

Nochum

---------- Original message ----------
From: Atul Vidwansa <Atul.Vidwa... at Sun.COM>
Date: Jan 8, 1:30 am
Subject: Newbie question: File locking, synchronicity, order, and ownership
To: lustre-discuss-list


Some comments inline..





Nochum Klein wrote:
> Hi Everyone,

> Apologies for what is likely a simple question for anyone who has been
> working with Lustre for a while.  I am evaluating Lustre as part of a
> fault-tolerant failover solution for an application component.  Based
> on our design using heartbeats between the hot primary and warm
> secondary components, we have four basic requirements of the clustered
> file system:

>    1. *Write Order *- The storage solution must write data blocks to
>       shared storage in the same order as they occur in the data
>       buffer.  Solutions that write data blocks in any other order
>       (for example, to enhance disk efficiency) do not satisfy this
>       requirement.
>    2.  *Synchronous Write Persistence* - Upon return from a
>       synchronous write call, the storage solution guarantees that all
>       the data have been written to durable, persistent storage.
>    3.  *Distributed File Locking* - Application components must be
>       able to request and obtain an exclusive lock on the shared
>       storage. The storage solution must not assign the locks to two
>       servers simultaneously.

AFAIK Lustre does support distributed locking. From wiki.lustre.org:

    * /flock/lockf/

    POSIX and BSD /flock/lockf/ system calls will be completely coherent
    across the cluster, using the Lustre lock manager, but are not
    enabled by default today. It is possible to enable client-local
    /flock/ locking with the /-o localflock/ mount option, or
    cluster-wide locking with the /-o flock/ mount option. If/when this
    becomes the default, it is also possible to disable /flock/ for a
    client with the /-o noflock/ mount option.

>    1.  *Unique Write Ownership* - The application component that has
>       the file lock must be the only server process that can write to
>       the file. Once the system transfers the lock to another server,
>       pending writes queued by the previous owner must fail.

It depends on what level of locking you do. Lustre supports byte-range
locking, so unless writes overlap, multiple writers can write to same file.

Cheers,
_Atul







>   1.

> Can anyone confirm that these requirements would be met by Lustre 1.8?

> Thanks a lot!

> Nochum
> ------------------------------------------------------------------------

> _______________________________________________
> Lustre-discuss mailing list
> Lustre-disc... at lists.lustre.org
>http://lists.lustre.org/mailman/listinfo/lustre-discuss

_______________________________________________
Lustre-discuss mailing list
Lustre-disc... at lists.lustre.orghttp://lists.lustre.org/mailman/listinfo/lustre-discuss
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lustre.org/pipermail/lustre-discuss-lustre.org/attachments/20100108/3d9d7351/attachment.htm>