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Jama 8 and XFS for Docker root directory

  • 1.  Jama 8 and XFS for Docker root directory

    Posted 04-26-2019 16:29
    I note that recent Jama installation documents contain this statement:

    Important

    For Docker's root directory, /var/lib/docker, an XFS filesystem degrades performance for container creation at startup. To avoid this, use EXT4 instead.

    Could someone clarify the detailed technical reason behind this recommendation?

    Is this, perhaps, related to the defaults when creating a new XFS fileysystem -- namely, that the XFS d_type feature is not enabled by default, which causes problems when using that XFS filesystem with the Docker overlay drivers?

    Or is the recommendation for some other reason?

    Thanks.


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    Ryan Dill
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  • 2.  RE: Jama 8 and XFS for Docker root directory

    Posted 04-26-2019 17:52
    Hi Ryan,

    Great question!

    You are completely correct. We do not recommend the XFS as it is formatted without d_type support, which leads to incorrect behavior.

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    Kimberly Embry
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  • 3.  RE: Jama 8 and XFS for Docker root directory

    Posted 04-26-2019 19:34
    Thanks, Kimberley.

    But that's just the *default* configuration of XFS, correct? Users may explicitly format the XFS volume with d_type support:

    i.e.

       mkfs.xfs -n ftype=1 /path/to/your/device

    where "ftype=1" enables d_type.

    Would doing so eliminate the "incorrect behaviour" wiith XFS, and make it OK to use with Jama?

    Also note that I believe "ftype=1" became the default as of RHEL 7.3 (https://access.redhat.com/solutions/3459291) -- so users creating new XFS filesystems from RHEL 7.3 onwards theoretically shouldn't see any incorrect behaviour.

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    Ryan Dill
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  • 4.  RE: Jama 8 and XFS for Docker root directory

    Posted 04-30-2019 14:07
    Hi Ryan,

    You're absolutely right. For RHEL 7.3+, ftype=1 is the default so you shouldn't see any incorrect behavior utilizing XFS. Between the two, XFS with ftype=1 is slightly more performant than EXT4. But the difference isn't necessarily notable, so for those on prior versions or for those less experienced with file system types, we recommend EXT4.

    For other viewers of this post, you can reference the Supported Backing Filesystems section on this article https://docs.docker.com/storage/storagedriver/select-storage-driver/ for more information.

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    Kimberly Embry
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  • 5.  RE: Jama 8 and XFS for Docker root directory

    Posted 04-30-2019 14:11
    Perfect -- thanks.

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    Ryan Dill
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