Re: Array of disks attached to multiple controllers

On Tue, Sep 14, 2004 at 04:07:43PM +0200, Lukas Kubin wrote:

     Chunk Size : 128K

(...)

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       2       8       48        2      active sync   /dev/sdd
       3       8       64        3      active sync   /dev/sde
       4       8       80        4      active sync   /dev/sdf
       5       8       96        5      active sync   /dev/sdg
       6       8      112        6      active sync   /dev/sdh
       7       8      128        7      active sync   /dev/sdi
       8       8      144        8      active sync   /dev/sdj
       9       8      160        9      active sync   /dev/sdk
      10       8      176       10      active sync   /dev/sdl
      11       8      192       11      active sync   /dev/sdm
      12       8      208       12      active sync   /dev/sdn
      13       8      224       13      active sync   /dev/sdo
      14       8      240       14      active sync   /dev/sdp
      15      65        0       15      active sync   /dev/sdq
      16      65       16       16      spare   /dev/sdr

I have a question about performance: What is the cost of writing a
'data-unit' in such an array?

- Write data: 1 write
- Calculate new checksum: 14 reads
- Write checksum: 1 write

Right or wrong?

What is the granularity of thoses ckecksum updates? 512 bytes (sector size)?
4k (page size on i386)? chunk-size?

Does Linux do read-ahead on thoses 14 disks reads?

Thanks

-- 
Seb, autocuiseur