On Thursday March 26, davidsen@xxxxxxx wrote: > I'm building a fairly aggressive machine for both a backup host for > virtual machines and spare time development platform, compile engine and > testbed both. I want to get cost effective use from an SSD unit, and I > propose to use a 32GB unit as follows: for the root filesystem, 12GB, > which should hold all the usual root things, and 16GB for swap (12GB > RAM, and I want boot and/or hibernate to happen NOW). The remaining > space I think might be used for various high impact things, and one of > those with speeding raid. > > 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? I'd probably just put the journal on the SSD and mount my ext3 filesystem data=journal That has a similar effect to raid1/write-behind in that data is written to both but we only wait for the write to the SSD to complete. But as it is done at the filesystem level - and the filesystem has a much better idea what it is doing - you would expect to get much more efficient results. e.g. less wasted memory, much larger amount of data that is safe of SSD but still trickling out to the HD. I guess there might be a small lost in data safety as is the journal device fails you lose your journal. But that is only 5 seconds of data, and I suspect SSDs don't suffer from many of the failure modes of HDs. .... I wonder if it would make sense to mirror two partitions of the one SSD?? It would save you from media errors and only expose you to total-drive-death errors. NeilBrown -- 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
