Re: Is partition alignment needed for RAID partitions ?

[Stan Hoeppner <stan@hardwarefreak.com>]

On 12/30/2013 7:05 PM, Pieter De Wit wrote:
> Hi Stan,
>> You're welcome.  Eventually you get to the bottom of this.
>>
> I think this moment has arrived :)
> 
> I did some fio tests from all levels, raw disk, raw md device, raw LV,
> filesystem (ext4) on top of LV. All read and write tests came back with
> +- 120MB/s (mostly 128, but let's tone it down just for stats)
> 
> I did a read,write and mixed test against the NAS:
> 
> The read and write tests came back at 60MB/s, the mixed came in at 11MB/s.

It seams clear the QNAP device is your weak link.

> I ran a network test from my desktop to the server, using iperf and it
> got up to 80MB/s, add to that the sync traffic of 10-15MB and you have a
> pretty full gig pipe. The desktop nic is a crappy onboard one, so I am
> quite happy with those stats. Just "FYI" - they are all linked with a
> Cisco 3750G, the NAS has 2xgig ports in an etherchannel

Etherchannel is proprietary to Cisco.  I'd be surprised if the QNAP
supports it.  802.11ad maybe, but not Etherchannel.  In any case it's
not relevant here as your pvmove operations are a single TCP stream.
Single streams always transmit over a single link, unless you have two
Linux hosts with 2 links each doing mode balance-rr with source based
routing.

> This leaves me only two conclusions:
> 
> 1) pvmove isn't as fast as I think - it might be due to some checksums
> or some other process (I know it creates a small mirror of a PE and then
> breaks it - rinse repeat for all PEs)

Try it between different disks within the host.  It should be much quicker.

> 2) That is just the limit for this system, "it is what it is"

I don't think the limit is your host but the QNAP.

> Either way - I think I have taken up enough of the list time, so thank
> you very much for the in-depth answers ! I still have access to the NAS
> until at least 13/01/2014 if you want to do more checks/tests.

More tests on the QNAP aren't necessary.  We already know it's slow.

> Have a good 2014!

You too.

-- 
Stan