On 04/10/13 17:21, Daniel Llewellyn wrote: > so it's effectively, if I understand this right. not redundant AT ALL > in terms of a disc dying and taking the data with it. Yes, it is. I think you don't understand it correctly :)
> AFAICT it saves two (or more) copies of each block, but it doesn't > ensure that those copies are on separate discs. so there could be 2 > mirrors of a block on the same drive thereby completely negating any > benefit for that particular block. I don't see where you get this idea? AFAICT pains are taken to ensure that duplicate chunks are written to separate devices. Otherwise, what exactly is the point at all? man md has more information on the layouts used, in its RAID 10 section. Nothing I see there implies that duplicate copies of a chunk can be written to the same device. > It also won't improve speed of read for that particular block because > if the drive is busy reading another block the system can't go to > "another disc" to get this block because it just ain't there. um, yes it is. > Likewise it will halve the write speed for this particular block > because it can't parallelise a write to each disc independently but > must queue the two copies for writing to the one disc sequentially. Once again, no. > In short, it's a completely flawed idea IMHO (of the Not So Humble > variety :-p) no, not really, it's just "different". Although I don't use it myself. -- Stuart Sears RHCA etc. "It's today!" said Piglet. "My favourite day," said Pooh. -- Please post to: Hampshire@mailman.lug.org.uk Web Interface: https://mailman.lug.org.uk/mailman/listinfo/hampshire LUG URL: http://www.hantslug.org.uk --------------------------------------------------------------
