Reserved Keywords & Offset Percentage

Reserved Keywords & Offset Percentage

[Gavin Martin]

Does Fio know the MaxLBA for devices it runs to?  If the size variable
has a percentage value, for example 50%, then it must have to read the
MaxLBA to know that on a 4TB drive the size of file we want is 2TB?
Is this correct or does it use another method?

If so would it be possible to have a reserved keyword for the MaxLBA,
much as you do currently for pagesize, memory & cpu's so that the size
& offset variable could make use of it, with the simple math
supported?

Not being a programmer and having very limited knowledge when it comes
to reading code, I have no idea if this is even possible within Fio?

If the above is not suitable, would it be possible for the offset
variable to accept percentages much like the size variable?

This comes from wanting to run Fio from dual hosts, I need to be able
to control which parts of the disk each host can access, so that they
do not interfere, on drives & ssds of many different sizes.

Basic example:

[Host 1]
size=50%
offset=0

[Host 2]
size=50%
offset 50%

Thanks,
Gavin

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Re: Reserved Keywords & Offset Percentage

[Jens Axboe]

On Thu, Mar 07 2013, Gavin Martin wrote:
> Does Fio know the MaxLBA for devices it runs to?  If the size variable
> has a percentage value, for example 50%, then it must have to read the
> MaxLBA to know that on a 4TB drive the size of file we want is 2TB?
> Is this correct or does it use another method?

That is correct, when adding files or devices, fio will check and store
the size of them.

> If so would it be possible to have a reserved keyword for the MaxLBA,
> much as you do currently for pagesize, memory & cpu's so that the size
> & offset variable could make use of it, with the simple math
> supported?

The problem here is that the current keywords are system wide specific,
whereas MaxLBA could refer to any particular device. So it would only
be valid within the scope of a single file.

> Not being a programmer and having very limited knowledge when it comes
> to reading code, I have no idea if this is even possible within Fio?
> 
> If the above is not suitable, would it be possible for the offset
> variable to accept percentages much like the size variable?
> 
> This comes from wanting to run Fio from dual hosts, I need to be able
> to control which parts of the disk each host can access, so that they
> do not interfere, on drives & ssds of many different sizes.
> 
> Basic example:
> 
> [Host 1]
> size=50%
> offset=0
> 
> [Host 2]
> size=50%
> offset 50%

Suppporting a percentage with offset would not be hard, but it would
only really work for a single file. For that, it would be doable.

-- 
Jens Axboe