Linux – Does software RAID-0 really improve performance

If you don't mind the cost, then there's nothing stopping you from RAIDing SSDs.

Always go with software RAID if you're not running a server! Software RAID is transferable between machines, and hardware RAID often isn't.

Personally, I wouldn't bother with RAID on the current generation of SSDs. Just get the one, and ensure you have sufficient backups that you don't feel concerned about loss of a drive. With the current price and size of SSDs it will be cheap and easy to back up, and then when they get cheaper and larger in the future (as they invariably will) I'd buy more :)

I'd also suggest looking at the MTBF of SSDs and hard disks, and calculating the chances of a failure (and the types of failure -- they may not be as catastrophic with SSDs, as a single sector breaking may not be a sign that the whole drive is dying as it can be with HDDs) and work out if the SSD has a higher or lower chance of failing than a set of RAIDed hard disks...

Edit : The official server fault blog says that this very site is going with RAID-ed SSDs now : http://blog.serverfault.com/post/our-storage-decision/

I think that "The LSI card does not have a BBU (yet) so write-back is disabled" is the bottleneck.

If you have UPS - enable the Write-Back.

If not - try to get the BBU.

If you can't - you can either risk the data consistency on the virtual drive by loosing the cached data in case of power surge if you enable Write-Back or stick to these speeds using write through cache.

Even if you align the partition to the logical volume (which is normally automatically done by most modern OSes) and format the volume with optimized cluster/block size big enough (i think it should be 2mb in your case) to get all the drives to process the single IO request i don't think you will achieve very big write performance difference.

Because the write performance of the RAID5 is very over-headed process. And since it is write through the XOR processor don't have the whole data in cache to perform the parity calculations in real time i think

With Write-Back enabled cache on 4x320gb hdds 515kb stip sized RAID 5 i get average 250-350 MB/s write speed writing big sequential files or average 150 MB/s copying big files inside the virtual volume. (i still don't have BBU but i have and old apc 700VA smart ups so i think its enough to minimize the power surges and eventual cache loss to a lot)

Are we discussing 100% random, 100% sequential or some mixed pattern? I am mostly experiencing high speeds when i fully read, write or copy big files on/from/to my array. On the other hand as already said random writes (reads) are much lower variating from less than 1 mb/s up to 190 mb/s average speeds depending on the file sizes and/or request sizes. Mostly under the 20mb/s range in everyday small size/file uses. So it depends a lot from the applications in the real life random transfers. As i am using windows OS my volumes are pretty mush as de-fragmented and for big files big operations like copying from/to are pretty fast

And one suggestion as a solution to the slow read/write random speeds of normal hdds - if you get to the point of reconfiguring your whole controller configuration why don't you consider CacheCade using 1 or 2 of the SSDs for no-power-dependent raid cache (something like the adaptec hybrid raids) and the rest for your OS/app drive as you are using them now? This way you should be able to boost the speed of your raid 5 volume even with write through i think because the actual write to the physical hdds should take place in the background and as you are using write through cache (no on board controller cache) and the ssds as cache instead i think you should be worry free of system resets. But for actual and concrete information on how cachecade works please read lsi's documentation and even ask LSI's technical support as i haven't got the chance to use it yet.