Why at least 4 cylinder groups?

[Peter Jeremy]

On 2016-Oct-11 08:50:44 +0200, Norbert Koch <nkoch at demig.de> wrote:
>Am 2016-10-10 um 17:26 schrieb Rodney W. Grimes:
>>> In an embedded system I am having a rather
>>> small (static) ram disk of about 1.5MB,
>>> formatted as UFS(1).

ufs2 is designed to work around some space limitations in ufs1 and so
needs more space.  If you're space-limited, ufs1 is probably a better choice.

>>> Is there any technical reason not to have less
>>> than 4 cylinder groups?
>> Probably on a UFS2 file system yes, but as far as I can
>> see not on a UFS1 file system.
>>
>>> For my application the wasted 188KB make a difference.
...
>So, afaics technically one cylinder group would be ok for UFS1, right?

The reasons for multiple CGs are:
1) Improve performance by limiting the seek distance to a CG.
2) Provide redundant superblocks to protect against bad blocks.
Neither of these reasons apply to a ramdisk.

If you're keen to maximise data space, you might like to also reduce
ipg (increase '-i').

-- 
Peter Jeremy
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