Fwd: Reverse Sequential Read or Write

Fwd: Reverse Sequential Read or Write

[Jay Han]

Hello,
I am trying to configure a sequential read or write pattern that reads
or writes in reverse manner in terms of LBAs. Is this feasible with
the features that are in current build? If so, any guidance would be
greatly appreciated.

Thank you,
Jay,

Re: Reverse Sequential Read or Write

[Ankit Kumar]

Hey Jan,

Replying again as the first one didn't go to the mailing list because
of that not being in plain text.

Yes, you can read/write in reverse order and there is already an
example fio configuration.
Check out:
https://github.com/axboe/fio/blob/master/examples/backwards-read.fio

Regards
Ankit


On Fri, Feb 3, 2023 at 10:58 PM Jay Han <jayhan258@gmail.com> wrote:
>
> Hello,
> I am trying to configure a sequential read or write pattern that reads
> or writes in reverse manner in terms of LBAs. Is this feasible with
> the features that are in current build? If so, any guidance would be
> greatly appreciated.
>
> Thank you,
> Jay,

Re: Reverse Sequential Read or Write

[Jay Han]

Thank you Ankit! I captured a trace using the example config file.
What does rw=read:-8k translate to in terms of LBA? I am seeing 4K seq
read in reverse manner. I am not sure what that 8k implies.
Each read is apart by 8. For example, the workload accessed LBAs
1540000, 1539992, 1539984, 1539976, 1539968, and so on.
Each read requested 8 logical blocks and the sector size is 512B which
makes up a 4K read.

Can you elaborate the -8K for me please?


On Fri, Feb 3, 2023 at 1:38 PM Jay Han <jayhan258@gmail.com> wrote:
>
> Thank you Ankit! I captured a trace using the example config file. What does rw=read:-8k translate to in terms of LBA? I am seeing 4K seq read in reverse manner. I am not sure what that 8k implies.
> Each read is apart by 8. For example, the workload accessed LBAs 1540000, 1539992, 1539984, 1539976, 1539968, and so on.
> Each read requested 8 logical blocks and the sector size is 512B which makes up a 4K read.
>
> Can you elaborate the -8K for me please?
>
>
>
> On Fri, Feb 3, 2023 at 11:07 AM Ankit Kumar <ankit1455@gmail.com> wrote:
>>
>> Hey Jan,
>>
>> Replying again as the first one didn't go to the mailing list because
>> of that not being in plain text.
>>
>> Yes, you can read/write in reverse order and there is already an
>> example fio configuration.
>> Check out:
>> https://github.com/axboe/fio/blob/master/examples/backwards-read.fio
>>
>> Regards
>> Ankit
>>
>>
>> On Fri, Feb 3, 2023 at 10:58 PM Jay Han <jayhan258@gmail.com> wrote:
>> >
>> > Hello,
>> > I am trying to configure a sequential read or write pattern that reads
>> > or writes in reverse manner in terms of LBAs. Is this feasible with
>> > the features that are in current build? If so, any guidance would be
>> > greatly appreciated.
>> >
>> > Thank you,
>> > Jay,

Re: Reverse Sequential Read or Write

[Vincent Fu]

On 2/3/23 16:17, Jay Han wrote:
> Thank you Ankit! I captured a trace using the example config file.
> What does rw=read:-8k translate to in terms of LBA? I am seeing 4K seq
> read in reverse manner. I am not sure what that 8k implies.
> Each read is apart by 8. For example, the workload accessed LBAs
> 1540000, 1539992, 1539984, 1539976, 1539968, and so on.
> Each read requested 8 logical blocks and the sector size is 512B which
> makes up a 4K read.
> 
> Can you elaborate the -8K for me please?
> 

The relevant documentation for the option in question is at the end of 
this section:

https://fio.readthedocs.io/en/latest/fio_doc.html#cmdoption-arg-readwrite

Basically fio is subtracting 8K from the end of each IO in order to get 
the next LBA to use.

Vincent

Re: Reverse Sequential Read or Write

[Jay Han]

Great, thank you very much, Vincent!

On Fri, Feb 3, 2023 at 3:35 PM Vincent Fu <vincentfu@gmail.com> wrote:
>
> On 2/3/23 16:17, Jay Han wrote:
> > Thank you Ankit! I captured a trace using the example config file.
> > What does rw=read:-8k translate to in terms of LBA? I am seeing 4K seq
> > read in reverse manner. I am not sure what that 8k implies.
> > Each read is apart by 8. For example, the workload accessed LBAs
> > 1540000, 1539992, 1539984, 1539976, 1539968, and so on.
> > Each read requested 8 logical blocks and the sector size is 512B which
> > makes up a 4K read.
> >
> > Can you elaborate the -8K for me please?
> >
>
> The relevant documentation for the option in question is at the end of
> this section:
>
> https://fio.readthedocs.io/en/latest/fio_doc.html#cmdoption-arg-readwrite
>
> Basically fio is subtracting 8K from the end of each IO in order to get
> the next LBA to use.
>
> Vincent