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| − | Draft squashfs/mountimg
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| − | == How can I use many small files efficiently? ==
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| − |
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| − | You can gain in performance and minimize the pressure under '''/data''' in
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| − | the following cases:
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| − | * '''case1''' your jobs are only reading under the directories where your zotfiles reside
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| − | * '''case2''' your jobs are reading your zotfiles but add only new files or directories in them
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| − | * '''case3''' your jobs generate zotfiles, but they will be accessed only for reading or adding new files afterwards
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| − |
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| − | For '''case1''':
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| − | * convert your zotfiles directories to squashfs images
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| − | * in your jobs:
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| − | ** mount those images using '''sudo mountimg'''
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| − | ** use those mounted directories for processing
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| − |
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| − | For '''case2''':
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| − | * convert your zotfiles directories to squashfs images
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| − | * in your jobs:
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| − | ** mount those images using '''sudo mountimg'''
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| − | ** use those mounted directories for processing but generate new files on the local filesystems of the node (ex: /tmp)
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| − | ** unmount the images with '''sudo mountimg -u'''
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| − | ** add the new files to the images with '''mksquashfs-no-compression'''
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| − |
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| − | For '''case3''':
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| − | * in your jobs:
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| − | ** generates your zotfiles on the local filesystems of the node (ex: /tmp)
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| − | ** convert them to squashfs images under '''/data''' with '''mksquashfs-no-compression'''
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| − |
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| − | === Creating squashfs images ===
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| − |
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| − | You can convert your zotfiles on '''nef-devel''' or '''nef-devel2'''.
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| − |
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| − | To convert your zotfiles to images, choose first the granularity
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| − | appropriate to your case.
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| − |
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| − | '''sudo mountimg''' allows actually to mount at most 4000 images on a node.
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| − |
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| − | If you have for example a really big directory /data/.../DDD/DD/
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| − | containing hundreds of sub-directories D1 D2 ... DN, you may prefer to
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| − | make one image per such sub-directory.
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| − |
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| − | Example (in bash):
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| − | cd /data/.../DDD
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| − | # Build a separate directory for the images and the mountpoints
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| − | mkdir DD-img DD-mnt
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| − | cd DD
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| − | for i in D*; do
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| − | # Create the image
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| − | mksquashfs-no-compression $i ../DD-img/$i.squashfs
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| − | # Create the mountpoint for your future jobs
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| − | mkdir ../DD-mnt/$i
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| − | done
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| − |
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| − | '''mksquashfs-no-compression''' is a simple wrapper to '''mksquashfs''' that
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| − | disable any kind of compression to focus on speed. Feel free to try
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| − | '''mksquashfs''' directly with other options like '''-comp lzo''' to
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| − | save disk space.
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| − |
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| − | Some mksquashfs hints:
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| − | * if the destination image exist, the source files/directories will be added (appended) to the image.
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| − | ** In addition, if a file/directory with a same name already exist in the image, the new file/directory will be added with the name xxx_1 xxx_2, etc, where xxx is the original name.
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| − | * If a single directory is specified (i.e. mksquashfs source output.squashfs) the squashfs filesystem will consist of that directory, with the top-level root directory corresponding to the source directory.
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| − | ** use the '''-keep-as-directory''' option to tell mksquashfs to keep the basename of the directory in its output.
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| − | * If multiple source directories or files are specified, mksquashfs will merge the specified sources into a single filesystem, with the root directory containing each of the source files/directories. The name of each directory entry will be the basename of the source path. If more than one source entry maps to the same name, the conflicts are named xxx_1, xxx_2, etc. where xxx is the original name.
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| − |
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| − | === Mounting squashfs images ===
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| − |
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| − | To mount one image, simply call: '''sudo mountimg <image path> <directory>'''
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| − |
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| − | To unmount: '''sudo mountimg -u <directory>'''
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| − |
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| − | Example: mount every squashfs images of /data/.../DDD/DD-img/ on the
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| − | corresponding sub-directory under /data/.../DDD/DD-mnt/
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| − |
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| − | cd /data/.../DDD/DD-mnt || exit
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| − | for i in *; do
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| − | sudo mountimg ../DD-img/$i.squashfs $i || exit
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| − | done
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| − |
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| − | In an oar job, a mount done with mountimg will be automatically
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| − | unmounted when the job terminates.
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| − |
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| − | Such a mount can also be shared by more than one oar job and by more
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| − | than one user. In this case, the unmount will be done when all the jobs
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| − | terminate. Beware that every job has to do this mount to register to
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| − | the list of processes needing it.
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| − |
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| − | mountimg allows actually to mount at most 4000 images on a node.
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