On Sat, Nov 22, 2014 at 8:22 AM, Anshuman Aggarwal <anshuman.aggarwal@xxxxxxxxx> wrote: > By not using stripes, we restrict writes to happen to just 1 drive and > the XOR output to the parity drive which then explains the delayed and > batched checksum (resulting in fewer writes to the parity drive). The > intention is that if a drive fails then maybe we lose 1 or 2 movies > but the rest is restorable from parity. > > Also another advantage over RAID5 or RAID6 is that in the event of > multiple drive failure we only lose the content on the failed drive > not the whole cluster/RAID. > > Did I clarify better this time around? I still don't understand the delayed checksum/parity. With classic raid 4, writing 1 GB of data to just D1 would require 1 GB of data first be read from D1 and 1 GB read from P then 1 GB written to both D1 and P. 4 GB worth of I/O total. With your proposal, if you stream 1 GB of data to a file on D1: - Does the old/previous data on D1 have to be read? - How much data goes to the parity drive? - Does the old data on the parity drive have to be read? - Why does delaying it reduce that volume compared to Raid 4? - In the event drive 1 fails, can its content be re-created from the other drives? Greg -- Greg Freemyer _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
