[lustre-discuss] EINVAL error when writing to a PFL file (lustre 2.12.0)

[Patrick Farrell]

Hmm.  I think because users can append to any file at any time, and also append to a file then write to it normally, we might override the users preferred layout for a file where appending is just a small part of the plan.  (And of course since we can’t control when users do append, it doesn’t let us handle the locking differently.)
________________________________
From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of Degremont, Aurelien <degremoa at amazon.com>
Sent: Friday, March 29, 2019 4:53:42 AM
To: Andreas Dilger; LEIBOVICI Thomas
Cc: lustre-discuss at lists.lustre.org
Subject: Re: [lustre-discuss] EINVAL error when writing to a PFL file (lustre 2.12.0)




    Another thought I just had while re-reading LU-9341 is whether it would be better to have the MDS always create files opened with O_APPEND with stripe_count=1?  There is no write parallelism for O_APPEND files, so having multiple stripes doesn't help the writer.  Because the writer also always locks the whole file [0,EOF] then there is no read-write parallelism either, so creating only a single file stripe simplifies things significantly with no real loss.

Having several stripes if still useful if you want to distribute space usage among several OSTs and also it could help if you have multiple readers later for this file.



Aurélien



    Cheers, Andreas

    On Feb 22, 2019, at 10:09, LEIBOVICI Thomas <thomas.leibovici at cea.fr> wrote:
    >
    > Hello Patrick,
    >
    > Thank you for the quick reply.
    > No, I have no particular use-case in mind, I'm just playing around with PFL.
    >
    > If this is currently not properly supported, a quick fix could be to prevent the user from creating such incomplete layouts?
    >
    > Regards,
    > Thomas
    >
    > On 2/22/19 5:33 PM, Patrick Farrell wrote:
    >> Thomas,
    >>
    >> This is expected, but it's also something we'd like to fix - See LU-9341.
    >>
    >> Basically, append tries to instantiate the layout from 0 to infinity, and it fails because your layout is incomplete (ie doesn't go to infinity).
    >>
    >> May I ask why you're creating a file with an incomplete layout?  Do you have a use case in mind?
    >>
    >> - Patrick
    >> From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of LEIBOVICI Thomas <thomas.leibovici at cea.fr>
    >> Sent: Friday, February 22, 2019 10:27:48 AM
    >> To: lustre-discuss at lists.lustre.org
    >> Subject: [lustre-discuss] EINVAL error when writing to a PFL file (lustre 2.12.0)
    >>
    >> Hello,
    >>
    >> Is it expected to get an error when appending a PFL file made of 2
    >> regions [0 - 1M] and [1M to 6M]
    >> even if writing in this range?
    >>
    >> I get an error when appending it, even when writting in the very first
    >> bytes:
    >>
    >> [root at vm0]# lfs setstripe  -E 1M -c 1 -E 6M -c 2 /mnt/lustre/m_fou3
    >>
    >> [root at vm0]# lfs getstripe /mnt/lustre/m_fou3
    >> /mnt/lustre/m_fou3
    >>    lcm_layout_gen:    2
    >>    lcm_mirror_count:  1
    >>    lcm_entry_count:   2
    >>      lcme_id:             1
    >>      lcme_mirror_id:      0
    >>      lcme_flags:          init
    >>      lcme_extent.e_start: 0
    >>      lcme_extent.e_end:   1048576
    >>        lmm_stripe_count:  1
    >>        lmm_stripe_size:   1048576
    >>        lmm_pattern:       raid0
    >>        lmm_layout_gen:    0
    >>        lmm_stripe_offset: 3
    >>        lmm_objects:
    >>        - 0: { l_ost_idx: 3, l_fid: [0x100030000:0x9cf:0x0] }
    >>
    >>      lcme_id:             2
    >>      lcme_mirror_id:      0
    >>      lcme_flags:          0
    >>      lcme_extent.e_start: 1048576
    >>      lcme_extent.e_end:   6291456
    >>        lmm_stripe_count:  2
    >>        lmm_stripe_size:   1048576
    >>        lmm_pattern:       raid0
    >>        lmm_layout_gen:    0
    >>        lmm_stripe_offset: -1
    >>
    >> [root at vm0]# stat -c %s /mnt/lustre/m_fou3
    >> 14
    >>
    >> * append fails:
    >>
    >> [root at vm0]# echo qsdkjqslkdjkj >> /mnt/lustre/m_fou3
    >> bash: echo: write error: Invalid argument
    >>
    >> # strace indicates that write() gets the error:
    >>
    >> write(1, "qsdkjqslkdjkj\n", 14)         = -1 EINVAL (Invalid argument)
    >>
    >> * no error in case of an open/truncate:
    >>
    >> [root at vm0]# echo qsdkjqslkdjkj > /mnt/lustre/m_fou3
    >>
    >> OK
    >>
    >> Is it expected or should I open a ticket?
    >>
    >> Thomas
    >>
    >> _______________________________________________
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    >> lustre-discuss at lists.lustre.org
    >> http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org
    >
    > _______________________________________________
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    Cheers, Andreas
    ---
    Andreas Dilger
    CTO Whamcloud




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