LFCS: Preparing Linux for nonvolatile memory devices [LWN.net]

LFCS: Preparing Linux for nonvolatile memory devices

Posted Apr 25, 2013 19:31 UTC (Thu) by Lennie (subscriber, #49641)
In reply to: LFCS: Preparing Linux for nonvolatile memory devices by rahvin
Parent article: LFCS: Preparing Linux for nonvolatile memory devices

As I read the story: the copying of the content of the DIMM to Flash will only happen at shutdown and read back in on poweron.

That would make it so that there is no overhead and the number of write and reads to flash are few in the life time of the module.

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LFCS: Preparing Linux for nonvolatile memory devices

Posted Apr 25, 2013 22:35 UTC (Thu) by rahvin (guest, #16953) [Link] (3 responses)

That seems somewhat limited functionality to me. Only seems to be functional in controlled shutdown type circumstances. It would seem to make more sense to make it a little more functional than only utilize it while the power is off.

LFCS: Preparing Linux for nonvolatile memory devices

Posted Apr 25, 2013 22:48 UTC (Thu) by Lennie (subscriber, #49641) [Link] (2 responses)

Controlled ?

I assume that it would have a storage of electricity (like a capacitor) which means when power is lost, it will start copying the data in DIMM to Flash.

The size of the Flash is a little larger than the DIMM (to have room for failed bits in Flash).

And it would have enough electricity to completely copy the content of the DIMM to Flash.

This is similar to a battery-backed RAID-controller with a write cache. When you do a write, the data is kept in RAM of the RAID-controller and the application gets an ACK that it is stored. On powerloss it will have enough electricity in a battery to write what is in RAM to the storage-devices.

So yes, it is controlled, but it is fully handled by the product because it is self-powered and does not rely on any other component.

LFCS: Preparing Linux for nonvolatile memory devices

Posted Apr 26, 2013 4:27 UTC (Fri) by rahvin (guest, #16953) [Link] (1 responses)

I apparently missed the capacitor statement in the article. But that would mean battery backup for more than just the DIMM though as you need some logic to manage the copy process. I can't help but think that is a server only type of installation.

LFCS: Preparing Linux for nonvolatile memory devices

Posted Apr 26, 2013 17:38 UTC (Fri) by Lennie (subscriber, #49641) [Link]

The article had server in the title and ASIC in text. So yes, probably.

And the ASIC hopefully also does some wear leveling to make sure it can always write to Flash.