Isilon: How to Identify Sparse Files on PowerScale OneFS
Summary: "A sparse file is a type of computer file that attempts to use file system space more efficiently when the file itself is partially empty. This is achieved by writing brief information (metadata) representing the empty blocks to disk instead of the actual "empty" space which makes up the block, using less disk space. " On Powerscale (Isilon) sparse files are identified by whether or not they have any sparse regions in the file. When a sparse region is written to a file there are no attributes/flags set but if the share has "sparse file support" enabled it will write the file as a sparse file. Credit: Wikipedia Sparse file article: https://en.wikipedia.org/wiki/Sparse_file ...
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Instructions
To identify if sparse file support is enabled for all new smb shares:
To identify if sparse file support is enabled on a specific share:
To check if a specific file is a sparse file (has sparse regions):
isi smb settings shares view --zone <zone name>|grep "Sparse File"
To identify if sparse file support is enabled on a specific share:
isi smb shares view --zone <zone name> <share name>|grep "Sparse File"
To check if a specific file is a sparse file (has sparse regions):
isi get -DDd /ifs/<path>|grep "sparse"
If this file contains a sparse region you should get output similar to this, where the number following the '#' represents how many blocks have been zero'd, also indicating there exists sparse blocks:
(sparse)#64 (sparse)#32
Additional Information
Note: When "sparse file support" is enabled for SMB this enables, the IOCTL SMB call FSCTL_SET_SPARSE, primarily for Commvault backup application usage, allows the backup client to "punch sparse holes" into the file, thus inserting sparse regions for compression purposes.
The support for sparse files over SMB is for FSCTL SET_ZERO_DATA for sparse hole punching only, for Commvault backups, other sparse file operations like ‘FSCTL_SET_SPARSE’ isn’t supported. OneFS will send a successful response to FSCTL_SET_SPARSE but does not set the sparse attribute/flag.
The support for sparse files over SMB is for FSCTL SET_ZERO_DATA for sparse hole punching only, for Commvault backups, other sparse file operations like ‘FSCTL_SET_SPARSE’ isn’t supported. OneFS will send a successful response to FSCTL_SET_SPARSE but does not set the sparse attribute/flag.
Article Properties
Article Number: 000192205
Article Type: How To
Last Modified: 26 Aug 2022
Version: 2
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