Re: mdadm raid6->LVM->ext4 setup

[Zoltan Szecsei <zoltans@geograph.co.za>]

On 2010-11-17 01:39, Michal Soltys wrote:
> On 10-11-16 23:17, Luca Berra wrote:
>> On Tue, Nov 16, 2010 at 08:08:44PM +0200, Zoltan Szecsei wrote:
>>>
>>> *** Commands used:
>>> mdadm --create /dev/md0 --metadata=1.2 --auto=md --assume-clean
>>> --bitmap=internal --bitmap-chunk=131072 --chunk=512 --level=6
>>> --raid-devices=8 /dev/sd[abcdefgh]
>>> mdadm --detail --scan >> /etc/mdadm.conf
>>> mdadm --assemble /dev/md0
>> as i said this is not useful
Accepted, but I also understood "not harmfull". I tried it out of 
curiosity, it took a nano-second to complete, so didn't try to "undo it".
>>> pvcreate --metadatasize 512 /dev/md0
>> you should use --dataalignment, not --metadatasize, also you should
I checked out man pvcreate & lvm.conf had all the stuff below in it, so 
I assumed it would sort itself out.
md_component_detection = 1
md_chunk_alignment = 1
data_alignment_detection = 1
data_alignment_offset_detection = 1

>
> Also with reference to metadatasize - keep in mind the value is 
> rounded up to the /next/ 64k boundary (or it was a while ago, perhaps 
> it's changed now). So in your case, 512 would really result with 576.
>
> With reference to --dataalignment - there's also --dataalignoffset 
> option (although not really important in your setup).
>
> You might consider adjusting 
> /sys/block/<yourmddevice>/md/stripe_cache_size to higher values when 
> you have everything set. It tends to give quite a performance boost.

I had trouble getting my head around all the calculations, mainly 
because I do not know if my sector size of 512 is falsely reported or 
not (so I just accepted it as 512).

I am loading the array as we speak, with 200MB to 400MB tiff files. In 
the past 11 hours approx 995GB was loaded, so that calculates to a write 
speed of 25MB/s

I have no problem stopping & deleting this if you feel that this 
represents problems in my setup, but then please can someone do the 
alignment calculations & command syntax for me.
Regards to all,
Zoltan







-- 

===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
P.O. Box 7, Muizenberg 7950, South Africa.

65 Main Road, Muizenberg 7945
Western Cape, South Africa.

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Tel: +27-21-7884897  Mobile: +27-83-6004028
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