performace increase=
good algorithm for minimal read/write time
+high speed disks (latency and read / write
time/unit(bit,byte,page), latency = time to head position at the right
sector, cilinder, etc etc, read/write speed = time to read/write a
block of bits/bytes/pages)
+ fast filesystem (without many writes like journaling... but
it´s not crash safe....)
+ faster memory caches (for read we could cache information that
don´t change... if it change on next read it will be cached)
see that:
filesystem is a upper level (not device level)
cache is a under level (operational system level, maybe raid cache,
maybe filesystem cache, maybe another cache)
high speed disk (a physical level)
algorithm (the raid level)
we could implement raid at filesystem (ok it´s not mdadm)... (brtfs if
i´m not wrong, and fuse raid system (a userspace raid software using
diferent filesystems))
since we want speed, get it closer to hardware (device) like md linux do
better than it just a dedicated hardware (faster than your cpu+memory+linux)
the problems are: more secure (file system/checksums/jornaling) = more
writes, more writes = more i/o, more i/o = more reads/writes = less
usefull information (file).
got?
2011/1/18 Igor Podlesny <for.poige+linux@xxxxxxxxx>:
> I had experience of using FreeBSD's vinum (another software RAID).
> Its author, Greg Lehey, stated in vinum's manual: "... A good
> guideline for stripe size is between 256 kB and 512 kB. Avoid powers
> of 2, however: they tend to cause all superblocks to be placed on the
> first subdisk. ..."
>
> Meanwhile, with LSR we're given exactly 2^n choices, for e. g.,
> neither 768 KiB, nor 387 KiB won't go: "mdadm: invalid chunk/rounding
> value: 387".
>
> So, why... ($Subj) and how complex would it be to abolish this
> restriction? I think this could be a key to performance increase.
>
> P. S. Thanks a ton for LSR, Neil, BTW. :-)
>
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--
Roberto Spadim
Spadim Technology / SPAEmpresarial
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