[GRASS-user] Splitting a location across several disks

[Blumentrath, Stefan]

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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