[LU-2580] cp with FIEMAP support creates completely sparse file

• Type: Bug
• Resolution: Fixed
• Priority: Blocker
• Affects Version/s: Lustre 2.3.0, Lustre 2.4.0
• Labels: LB
• Environment: SLES 11 SP2 (client), Lustre 2.1.2 RHEL6 (server)
• Severity: 2
• Assignee: Peter Jones
• Reporter: Kit Westneat (Inactive)

Description

We are seeing an issue at KIT where cp will occasionally use the FIEMAP extension to create a completely sparse file instead of actually copying the file. It seems to occur under a workload involving creating and deleting many files at once. It only involves a single client though, it's not a parallel workload.

Relevant strace from 'bad' cp:
ioctl(3, 0xc020660b, 0x7fff392c0950) = 0
ftruncate(4, 12853) = 0

strace from 'good' cp:
read(3, "#!/bin/bash -u\n\n#localisation\nex"..., 2097152) = 12853
write(4, "#!/bin/bash -u\n\n#localisation\nex"..., 12853) = 12853
read(3, "", 2097152) = 0

The strace didn't print the stat block information, but I'm assuming the st_blocks == 0 in the bad one. I will ask the customer to get a full strace -v to confirm, but it appears to be something similar to LU-417?

Issue Links

• is related to: LU-3219 FIEMAP does not sync data or return cached pages
• is related to: LU-417 block usage is reported as zero by stat call for tens of seconds after creating a file