COncurrent access to shared disk library

Last post 04-20-2017, 4:50 PM by jjbiv. 3 replies.
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  • COncurrent access to shared disk library
    Posted: 04-19-2017, 3:11 AM


    I have used shared disk libraries in a very asynchronous manner to move backups around on portable media.  This works very well.

    I am looking to create a shared library that can be active on multiple media agents at once. 

    There is plenty of documentation for configuring same but what I want to understand is the matter of *CONCURRENT* access via different media agents.

    Shared libraries are managed by creating mount paths to the same storage on different MAs.  THis is at the FS level and thus concurrency requires distributed file locking of some sort (as well as both MAs having the ability to read that FS)

    I imagine I could use NFS although I would still need a coordination process between all elements to ensure the scheduling of IO is sane.  Will an NFS-based library work this way?  Context : I may not be able to use NFS here, hence the following questions.

    But does Simpana have some sort of native ability to manage concurrent access to the same storage?

    What about third party clustered FS?

    I see a licence option called shared storage.  I am not sure what this is.  Note : I am NOT talking about clustered media agents (though that is an interesting sub-topic in itself)

    Or does Simpana simply enforce serialised access to shared storage, as for tape drives?





  • Re: COncurrent access to shared disk library
    Posted: 04-19-2017, 8:01 PM

    Hi SF,

    For disk storage, Commvault manages concurrent access natively by automatically creating sub-folders/directories on the shared storage and providing each MA with exclusive access to a folder while it is being used. Thus, two MAs should never try to write to the same file at the same time. For tape devices, Commvault ensure only one MA is writing to a drive at a time.

    You might be interested in ScaleOut Storage Pool, too. There are some very interesting possibilities to create your own scale-out disk library with that feature.

  • Re: COncurrent access to shared disk library
    Posted: 04-19-2017, 9:43 PM

    Thanks jjbiv.

    That seems a logical approach however, if I have a directory tree for MA #1 and another tree for MA#2 I can enforce separation of access to data content but the two MAs still need to mount the same filesystem at the same time and IO (to two different directory trees) will still land on that same filesystem at the same time (potentially).

    Unless there is a cluster filesystem (or similar) in place, then it seems to me that the only way Simpana can manage this is to enfore separation at the directory tree level and also to block access by one MA to the mount path itself whilst the other MA is doing its thing.  But even if it does that, most standard filesystems cannot be mounted concurrently on two servers at once.

    The scaleout pool sounds very cluster-ish (or a smoke-n-mirrors approach like Oracle Solaris Cluster GlobalFS) but I am not sure it is what I want.

    I think I am missing something obvious here!!!!



  • Re: COncurrent access to shared disk library
    Posted: 04-20-2017, 4:50 PM

    You are correct: the underlying file system needs to support concurrent access to the storage volume. This is one advantage of using NAS, object storage, or clustered file systems vs. locally attached block storage.

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