Re: LVM on raid10,f2 performance issues

[Bill Davidsen <davidsen@tmr.com>]

Peter Rabbitson wrote:
> thomas62186218@aol.com wrote:
>   
>> Hi everyone,
>>
>> I too was seeing miserable read-performance with LVM2 volumes on top of
>> md RAID 10's on my Ubuntu 8.04 64-bit machine. My RAID 10 has 12 x 300GB
>> 15K SAS drives on a 4-port LSI PCIe SAS controller.
>>
>> I use:
>> blockdev --setra 65536 /dev/md0
>>
>> And this dramatically increased my RAID 10 read performance.
>>
>> You MUST do the same for your LVM2 volumes for them to see a comparable
>> performance boost.
>>
>> blockdev --setra 65536 /dev/mapper/raid10-testvol
>>
>>     
>
> This is incorrect. Only the readahead setting of the _last_ block device
> matters. So in case you have a raid6 of 10 drives, with LUKS on top,
> with LVM on top - only the readahead settings of the individual LVs
> matter, nothing further down the chain is consulted.

I have some old numbers which indicate that with ext3 the use of 
"stride=" can improve performance, although I was measuring write and 
just got the read numbers without really caring about them.

-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark