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[BUG] No "empty" chinks in empty file. #644

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@onlyjob

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@onlyjob

I have a (old) large mostly empty file created on MooseFS v3. mfsfileinfo shows that it have "empty" chunks like this:

        chunk 7: empty
        chunk 8: empty
        chunk 9: empty

On current MooseFS 4.56.6, I'm trying to reproduce that by making a large empty file:

$ fallocate -l 8g 8GiB_empty.raw
fallocate: fallocate failed: Operation not supported

Ops, I wish that worked but no worries, I've made that empty file on local file system then moved it to MFS.
(File is in storage class 2.)

Now:

$ mfsfileinfo -c  8GiB_empty.raw
8GiB.empty:
        chunk 0: 000000004C04AB65_00000001 / (id:1275374437 ver:1) ; mtime:1740547377 (2025-02-26 16:22:57)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 1: 000000004C04AB66_00000001 / (id:1275374438 ver:1) ; mtime:1740547377 (2025-02-26 16:22:57)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 2: 000000004C04AB67_00000001 / (id:1275374439 ver:1) ; mtime:1740547377 (2025-02-26 16:22:57)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 3: 000000004C04AB68_00000001 / (id:1275374440 ver:1) ; mtime:1740547377 (2025-02-26 16:22:57)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 4: 000000004C04AB69_00000001 / (id:1275374441 ver:1) ; mtime:1740547378 (2025-02-26 16:22:58)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 5: 000000004C04AB6A_00000001 / (id:1275374442 ver:1) ; mtime:1740547378 (2025-02-26 16:22:58)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 6: 000000004C04AB6B_00000001 / (id:1275374443 ver:1) ; mtime:1740547378 (2025-02-26 16:22:58)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 7: 000000004C04AB6C_00000001 / (id:1275374444 ver:1) ; mtime:1740547378 (2025-02-26 16:22:58)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 8: 000000004C04AB6D_00000001 / (id:1275374445 ver:1) ; mtime:1740547378 (2025-02-26 16:22:58)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 9: 000000004C04AB6E_00000001 / (id:1275374446 ver:1) ; mtime:1740547378 (2025-02-26 16:22:58)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
        chunk 10: 000000004C04AB6F_00000001 / (id:1275374447 ver:1) ; mtime:1740547379 (2025-02-26 16:22:59)
                copy 1: 192.168.0.204:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
                copy 2: 192.168.0.250:9422 ; status:VALID ; blocks: 1024 ; checksum digest: 0486CB73567D30B815495C919B929A9E
... etc.

But all those chunks should be "empty", without any chunk files.

(For what it's worth, all my chunkservers are configured with HDD_SPARSIFY_ON_WRITE = 1 but that shouldn't matter.)

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