On 2 July 2016 at 20:49, Richard Scobie <r.scobie@xxxxxxxxxxxx> wrote:
>
> Nick Fisk wrote:
>
> "So it looks like each parallel IO thread is being
> allocated next to each other rather than at spaced out regions of the disk."
>
> It's possible that the "filestreams" XFS mount option may help you out. See:
>
>
> http://www.xfs.org/docs/xfsdocs-xml-dev/XFS_User_Guide/tmp/en-US/html/ch06s16.html
Thanks, I will see if this helps. Should I have any concern about
ongoing IO once the VM has been copied? That link seems to suggest
problems if the file is appended again at a later date. I believe the
holes shown below are due to it being a sparse file.
Would also using swalloc and a large swidth have any effect, or is
this like the allocsize, ignored once the file is closed?
I've been doing a bit more digging and I think the problem is a bit
more complex than I first thought. ESX seems to multithread the copy
with lots of parallel 64kb io's, I believe looking at xfs_bmap that
some these threads are also getting written out of order, which
properly isn't helping, although this is probably a minor problem in
comparison. This example file is 40GB and has nearly 50,000 extents.
0: [0..127]: 5742779480..5742779607 128 blocks
1: [128..2047]: hole 1920 blocks
2: [2048..2175]: 5742779736..5742779863 128 blocks
3: [2176..2303]: 5742779608..5742779735 128 blocks
4: [2304..2431]: 5742779864..5742779991 128 blocks
5: [2432..4351]: hole 1920 blocks
6: [4352..4607]: 5742779992..5742780247 256 blocks
7: [4608..12543]: hole 7936 blocks
8: [12544..12671]: 5742780248..5742780375 128 blocks
9: [12672..13695]: 5742798928..5742799951 1024 blocks
10: [13696..13823]: 5742813392..5742813519 128 blocks
11: [13824..13951]: 5742813648..5742813775 128 blocks
12: [13952..14079]: 5742813264..5742813391 128 blocks
13: [14080..14207]: 5742813520..5742813647 128 blocks <-- Next
to 10 on disk
14: [14208..14719]: 5742813776..5742814287 512 blocks <-- Next
to 11 on disk
15: [14720..15359]: 5742837840..5742838479 640 blocks
16: [15360..15487]: 5743255760..5743255887 128 blocks
17: [15488..15743]: 5742838608..5742838863 256 blocks
18: [15744..15871]: 5743133904..5743134031 128 blocks
19: [15872..15999]: 5743134288..5743134415 128 blocks
20: [16000..16127]: 5743255632..5743255759 128 blocks
21: [16128..16255]: 5743133776..5743133903 128 blocks
22: [16256..16383]: 5743134032..5743134159 128 blocks
23: [16384..16511]: 5742838480..5742838607 128 blocks
24: [16512..16895]: 5743255888..5743256271 384 blocks
25: [16896..17023]: 5743134416..5743134543 128 blocks
26: [17024..17151]: 5743134160..5743134287 128 blocks
Thanks,
Nick
>
> Regards,
>
> Richard
>
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