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 <[email protected]> on behalf of
Degremont, Aurelien <[email protected]>
Sent: Friday, March 29, 2019 4:53:42 AM
To: Andreas Dilger; LEIBOVICI Thomas
Cc: [email protected]
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 <[email protected]> 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 <[email protected]> on behalf
of LEIBOVICI Thomas <[email protected]>
>> Sent: Friday, February 22, 2019 10:27:48 AM
>> To: [email protected]
>> 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@vm0]# lfs setstripe -E 1M -c 1 -E 6M -c 2 /mnt/lustre/m_fou3
>>
>> [root@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@vm0]# stat -c %s /mnt/lustre/m_fou3
>> 14
>>
>> * append fails:
>>
>> [root@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@vm0]# echo qsdkjqslkdjkj > /mnt/lustre/m_fou3
>>
>> OK
>>
>> Is it expected or should I open a ticket?
>>
>> Thomas
>>
>> _______________________________________________
>> lustre-discuss mailing list
>> [email protected]
>> http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org
>
> _______________________________________________
> lustre-discuss mailing list
> [email protected]
> http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org
Cheers, Andreas
---
Andreas Dilger
CTO Whamcloud
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