RAID10 not working in install

Bill Davidsen davidsen at
Wed Feb 27 21:05:09 UTC 2008

Mike Wright wrote:
> Bill Davidsen wrote:
>> Alan Cox wrote:
>>>> The raw read speed on a RAID1 array is the speed of a single drive. 
>>>> The     
>>> No. A smart raid1 driver will use both source disks. The raw write speed
>>> is that of the slowest drive (plus overhead).
>> Does this mean that the Linux software RAID is not smart, or there's a 
>> way to make it actually do this?  Current FC[678] doesn't seem to be 
>> "smart."
>>> RAID 10 gives you better write throughput which on a modern PC normally
>>> means that with PCI Express your bridge/memory bandwidth becomes the
>>> limit.
>> This is what I measure running an E6600 CPU and 3xSeagate 320 with 
>> Recent FC7 kernel. All reads and writes to the raw array using dd, 1MB 
>> buffer, 1GB i/o to/from /dev/{zero,null} for raw speed. Units are 
>> MB/s, 64k chunks, speed as reported by dd.
>> RAID lvl        read        write
>> 0               110         143
>> 1                52.1        49.5
>> 10               79.6        76.3
>> 10f2            145          64.5
>> raw one disk     53.5        54.7
> Sorry to butt in but what does 10f2 mean/stand for?
Array creates with two "far" copies. See "man mdadm" and search the "-p" 
option for near, far, and offset disk layout. The "far" layout has been 
giving me great read speeds, which is (in most cases) more important 
than write, since writes can be cached but when the program is waiting 
for data it stops. Readahead isn't a substitute for throughput if you 
read BIG data.

Bill Davidsen <davidsen at>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

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