Hi, William, William Yu wrote:
> Random write performance (small block that only writes to 1 drive): > 1 write requires N-1 reads + N writes --> 1/2N-1 % This is not true. Most Raid-5 engines use XOR or similar checksum methods. As opposed to cryptographic checksums, those can be updated and corrected incrementally. check_new = check_old xor data_old xor data_new So 2 reads and 2 writes are enough: read data and checksum, then adjust the checksum via the data difference, and write data and new checksum. And often, the old data block still is in cache, accounting to 1 read and two writes. HTH, Markus -- Markus Schaber | Logical Tracking&Tracing International AG Dipl. Inf. | Software Development GIS Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
