3TB disc and block alignment

Mark Felder feld at feld.me
Wed Feb 23 15:40:04 UTC 2011

On Mon, 21 Feb 2011 10:16:37 -0600, Kurt Jaeger <lists at c0mplx.org> wrote:

> Hi!
>> > Hmm, wasn't the issues with 3T drives, that they internally use
>> > 4K blocks and emulate 512 and that therefore 8 block alignments
>> > are an performance issue ?

Hi guys,

I'd just like to jump on this train real quick since I have a related  
question with alignment.

I've been building new Virtual Machine templates lately because I recently  
learned that our SAN which we access over iSCSI uses 64K blocks and the  
default FreeBSD install starts a filesystem on sector 63 (512K sectors).  
This would be misaligned for most I/O transactions. As a result, I updated  
our internal documentation for FreeBSD standards to be 64K aligned by  
manually installing FreeBSD with GPT and making the FreeBSD-boot partition  
64K in size:

Fixit# gpart create -s gpt da0
Fixit# gpart add -t freebsd-boot -s 64K da0
Fixit# gpart add -t freebsd-swap -s 2G -b 2048 da0
Fixit# gpart add -t freebsd-ufs da0
Fixit# gpart bootcode -b /dist/boot/pmbr -p /dist/boot/gptboot -i 1 da0

At the time, the examples I found used -s 64K for the freebsd-boot  
partition which starts the next partition/filesystem on the next 64K block  
which would be aligned for our purposes. However, I have been seeing -s  
1024K or larger which is also 64K aligned, but just larger. Am I shooting  
myself in the foot by not going ahead and aligning with -s 1024K or -s  
2048K right now?

Thanks for your opinions,


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