[GRASS-user] Splitting a location across several disks

[Dylan Beaudette]

Thanks, this is quite helpful. I'll report back with my strategy and
any limitations of this approach.

On Wed, Oct 7, 2015 at 11:43 PM, Blumentrath, Stefan
<Stefan.Blumentrath at nina.no> wrote:
> See also: https://grasswiki.osgeo.org/wiki/Location_and_Mapsets
> There you find a detailed description of how to link mapsets...
>
> -----Original Message-----
> From: grass-user-bounces at lists.osgeo.org [mailto:grass-user-bounces at lists.osgeo.org] On Behalf Of Dylan Beaudette
> Sent: 8. oktober 2015 00:50
> To: Glynn Clements <glynn at gclements.plus.com>
> Cc: grass list <grass-user at lists.osgeo.org>
> Subject: Re: [GRASS-user] Splitting a location across several disks
>
> On Wed, Oct 7, 2015 at 3:39 PM, Glynn Clements <glynn at gclements.plus.com> wrote:
>>
>>
>> Dylan Beaudette wrote:
>>
>> > It has been a while, but glad to be back on GRASS-user.
>> >
>> > I am working on a project that involves a significant storage
>> > dilemma: try and fit most of the files into a 500 Gb SSD for
>> > blazing-fast I/O, or fall back to a standard but higher capacity disk drive.
>> >
>> > Would it be possible to store "derived" data into a mapset that is
>> > on standard disk, while the "source" data reside in another mapset,
>> > stored on the SSD?
>> >
>> > In other words, is it OK for a location to contain several mapsets
>> > that don't "live" on the same physical disk. It seems like it should
>> > work (via symlink), but I would like to see if there are any caveats
>> > that I should be aware of.
>>
>> If symlinks don't work, Linux supports "mount --bind ...", which lets
>> you mount a directory from an already-mounted filesystem at another
>> location. Windows has similar features (e.g. reparse points), although
>> I'm not that familiar with the specifics.
>>
>
> Excellent! This is the answer that I was looking for. I will try symlinks first, otherwise the "mount --bind" strategy is simple enough. Fortunately this work will be done on linux so just about anything is possible.
>
>>
>> The main constraint is that you can't split a single mapset across
>> devices, as it must be possible to rename() files in the .tmp
>> subdirectory to other directories withing the mapset, which requires
>> that they are on the same physical partition (rename() only
>> manipulates directory entries, it won't move the file's data blocks).
>
> OK, good to know.
>
> Is there any reason to think that reading lots of raster files will be noticeably faster on the SSD?
>
> Thanks,
> Dylan
>
>> --
>> Glynn Clements <glynn at gclements.plus.com>
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