bugGNU tar - Bugs: bug #66559, No option to preallocate files

 
 

bug #66559: No option to preallocate files

Submitter:  David W <dmw>
Submitted:  Fri 13 Dec 2024 01:38:17 AM UTC
   
 
Category:  None Severity:  3 - Normal
Item Group:  None Status:  None
Privacy:  Public Assigned to:  None
Open/Closed:  Open
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Fri 13 Dec 2024 01:38:17 AM UTC, original submission:  

Please consider an option to have tar call fallocate(2) prior to extraction, to give the underlying filesystem a chance to allocate contiguous space for each file.

This is motivated by investigation of performance problems on a SMR disk, and discovering that during the most recent tar extraction, thousands of small (<60mb) files were created such that they almost always occupied multiple ext4 extents, and the physical start offsets of those extents almost always occurred within different shingle zone boundaries, leading to a situation where writing one 60mb file would lead the disk to reading/modifying/rewriting data in as much as 512mb of shingles.

There is a similar discussion open for GNU cp, which pointed out this behaviour could not (as of circa 2011) be the default behaviour there, as at least XFS conflates preallocation requests with some more exotic fs-specific semantics.

David W <dmw>

 

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