Re: RAIDframe and alignment on 4K-sector disks?

[mlelstv%serpens.de@localhost (Michael van Elst)]

jdbaker%mylinuxisp.com@localhost ("John D. Baker") writes:

>Doesn't RAIDframe assume 512-byte sectors?  So, 64k stripe size would
>be SecPerSU=128, yes?

SecPerSU * StripeUnits = StripeSize

A 64k stripe is the maximum that you can access with a single I/O
operation (maxphys). A RAID-5 with 3 disks splits a 64k stripe into
2 stripe units of 32k.


>> -> format the filesystem(s) with 64k blocks and 8k fragments (64k fragments
>>    might be faster sometimes but waste disk space).

>If one is making blocks=stripes, won't a single 8k fragment write provoke
>an RMW operation at the RF level (operate on less than a full stripe)?

It does. But that's a fragment, the last bit of a file.


>I seem to recall another strategy to make frags=stripes so the minimal

With 64k blocks and 64k stripes you would need 64k frags. I.e. no
fragmentation. This wastes some space. Of course you could reduce
the stripe size below block size, but that increases overhead.



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                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."