[Nottingham] Large disks and storage (md raid)

[Martin]

Martin wrote:
> Martin wrote:
>>> ... md raid1/raid10f2/raid5 :)
>> Which comes to another question... :-)
>>
>>  From "man 8 mdadm":
>>
>> "Use the new version-1 format superblock. This has few restrictions. The 
>> different subversion store the superblock at different locations on the 
>> device, either at the end (for 1.0), at the start (for 1.1) or 4K from 
>> the start (for 1.2)."
>>
>>
>> So...
>>
>> Why would you want the raid superblock to be 4k from the start?
>>
>> And for the sake of ssd/stripe alignment, how big is the superblock?
>>
>> Why not simply have the superblock at the end (v1.0)?

...And that lot is mostly answered in:

http://wiki.tldp.org/LVM-on-RAID

The more recent versions of LVM also now include an option to auto-align 
to the stripes of an underlying raid device.

And there's enough detail there to help with aligning to the erase 
blocks of SSDs and flash memory sticks.

Nicely written.

I wonder if LVM was updated in response to Theodore Ts'o's rant about 
LVM's "slightly baroque" way of alignment for the metadata size:

http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size/


So... Looks like raid1 with a v1.0 superblock is the way to go!

... Or does a v1.2 superblock fit nicely after a partition table (on 
track 0) yet before the start of the first partition if placed on the 
old DOS required track 1 start?

?

Cheers,
Martin


-- 
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Martin Lomas
martin at ml1.co.uk
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