(SOLVED) Re: installing FreeBSD 8 on SSDs and UFS2 - partition alignment, block sizes, what does one need to know?

Dan Naumov dan.naumov at gmail.com
Fri Jan 15 16:57:15 UTC 2010

On Fri, Jan 15, 2010 at 6:38 PM, Rick Macklem <rmacklem at uoguelph.ca> wrote:
> On Tue, 12 Jan 2010, Dan Naumov wrote:
>> For my upcoming storage system, the OS install is going to be on a
>> 80gb Intel SSD disk and for various reasons, I am now pretty convinced
>> to stick with UFS2 for the root partition (the actual data pool will
>> be ZFS using traditional SATA disks). I am probably going to use GPT
>> partitioning and have the SSD host the swap, boot, root and a few
>> other partitions. What do I need to know in regards to partition
>> alignment and filesystem block sizes to get the best performance out
>> of the Intel SSDs?
> I can't help with your question, but I thought I'd mention that there
> was a recent post (on freebsd-current, I think?) w.r.t. using an SSD
> for the ZFS log file. It suggested that that helped with ZFS perf., so
> you might want to look for the message.
> rick

I have managed to figure out the essential things to know by know, I
just wish there was a single, easy to grasp webpage or HOWTO
describing and whys and hows so I wouldn't have had had to spend the
entire day googling things to get a proper grasp on the issue :)

To (perhaps a bit too much) simplify things, if you are using an SSD
with FreeeBSD, you:

1) Should use GPT

2) Should create the freebsd-boot partition as normal (to ensure
compatibility with some funky BIOSes)

3) All additional partitions should be aligned, meaning that their
boundaries should be dividable by 1024kb (that's 2048 "logical blocks"
in gpart). Ie, having created your freeebsd-boot, your next partition
should start at block 2048 and the partition size should be dividable
by 2048 blocks. This applies to ALL further partitions added to the
disk, so you WILL end up having some empty space between them, but a
few MBs worth of space will be lost at most.

P.S: My oversimplification was in that MOST SSDs will be just fine
with a 512 kb / 1024 block alignment. However, _ALL_ SSDs will be fine
with 1024 kb / 2048 block alignment.

- Sincerely,
Dan Naumov

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