Re: IIs factible to implement full writes of strips to raid using NVRAM memory in LFS?

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Thu, Aug 18, 2016 at 06:23:32PM +0000, Eduardo Horvath wrote:
> 
> I suppose adding code to LFS where it posts the sync write to copy 
> it out to NVRAM would be relatively easy.

Perhaps, but I bet it'd be easier to implement a generic pseudodisk
device that used NVRAM (fast SSD, etc -- just another disk device really)
to buffer *all* writes to a given size and feed them out in that-size
chunks.  Or to add support for that to RAIDframe.

For bonus points, do what the better "hardware" RAID cards do, and if
the inbound writes are already chunk-size or larger, bypass them around
the buffering (it implies extra copies and waits after all).

That would help LFS and much more.  And you can do it without having
to touch the LFS code.

However, there's stll the issue that this could effectively reorder
reads around synchronous writes if you are not careful, particularly
with the boot-time replay.  Ensuring that is right is probably the
trickiest part by far.

Thor