On Thursday March 26, drees76@xxxxxxxxx wrote: > On Thu, Mar 26, 2009 at 4:09 PM, Bill Davidsen <davidsen@xxxxxxx> wrote: > > If I were to create a small raid device, raid1, made of the 4GB Ssd and 4GB > > of SATA space, if I made the SATA write-mostly and write-behind, and put the > > journal for my raid arrays (and bitmaps?) that seems likely to provide a > > significant performance gain in small storage. > > > > Am I missing anything here? Is there an obvious drawback I'm missing? > > Yeah, the fact that it doesn't seem to be possible to take advantage > of the write-behind feature? :-p > > Besides fsync, I think it may have something to do with barriers. As > in, when you flush a barrier, that causes entire cache to get flushed > to disk, including your write-behind disk. Nope. The barriers are sent separately to both devices. Yes, they both get flushed, but we don't wait for the write-behind flush to complete. NeilBrown > > Hopefully Neil can chime in here. I found this thread from a while > back which seemed relevant, but I haven't been able to digest the > whole thing yet: http://lkml.org/lkml/2007/5/25/71 > > -Dave > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
