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[dm-devel] Could device-mapper offer multi-tier storage?

Hi all,

I'm seeing a good bit of interest in multi-tier storage in high end systems, and was wondering if this functionality could be offered by device-mapper.

By multi-tier, I'm speaking of systems where various speed/quality storage units are used in an analogous way to the way cache is used for memory: The most recently/often used data blocks are placed on the fastest storage device, then over time gets flushed out to slower systems. It seems the trend is to use a smaller array of 15k rpm SAS drives as the first tier, then flush it out to much larger arrays of 7200 rpm SATA drives as the second tier.

While this clearly has benefits in large systems, I would think the same concept could be brought in-box as well, by using a fast 15k or solid state drive as the first tier, and then pushing out to 7200 rpm SATA as a second tier. My interest is more in the large system side, but if this functionality was available and easy to use, I could see it getting wide adoption in smaller systems too -- just as RAID was once limited to big systems, this could be a cool technology to make available to all.

So the questions:

1)  Is device-mapper the right layer to look at applying this?

2)  If so, any ideas on how hard it would be to implement?

3) If device-mapper is not the right place, any idea where this functionality should go, or if it is already out there in another form?

Thanks -- I would love to hear any thoughts or questions on this.


 Ty! Boyack
 NREL Unix Network Manager
 ty nrel colostate edu
 (970) 491-1186

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