[Nottingham] SSDs

[Martin]

On 24/02/12 23:25, Camilo Mesias wrote:
[---]
> 
> I appreciate the silence and the speed. 60Gb is more than enough for a
> Linux distro, but if there are better deals on larger ones, I would be
> tempted as they might last longer.

I also very much appreciate the lack of noise. The low power operation
is another good plus. For laptop/netbook use, the no-moving-parts (as
compared to a rotating HDD) is very reassuring for when going travelling...

As for getting what SSD from where, note that there is a large variation
in capability between the various generations of flash controllers and
for even what firmware is used. I would recommend checking out at least
two reviews on the specific drive you're thinking of getting and
comparing against the current generation.

If you really want cheap-and-don't-care, then just use a USB memory
stick! With a little care, I've had over two years 24/7 use out of some
without problem. Without any care, I've also destroyed two after just
three months :-(


> I avoided a swap partition. After rough benchmarks I ditched LVM. I
> made sure trim was working.

Very good moves!


> I checked my netbook chipset was specced to run fast enough to make
> the most of the drive's speed (it does SATA II so up to 3Gb/sec, about
> right and certainly not worth getting any faster SSD; if the chipset
> only did SATA I then I would be wasting my money).

For 'normal' use, all the current SSDs /should/ be more than fast
enough... Just watch out for SATA/SATA-II and SATA-II/SATA3
compatibility. Some older SSDs have jumpers to select what speed. Newer
SSDs automatically detect.


> There have been some doubts cast over the OCZ benchmark specs, I
> wouldn't be surprised if all manufacturers did similar things though:
> 
> http://www.theregister.co.uk/2011/01/14/ocz_and_ddrdrive_performance_row/

That is a good example for a worse case contrast against the marketing
claimed specs. A good explanation is given in the comment:

http://forums.theregister.co.uk/post/957933



For more than you'll likely want to know, there's a 'work in progress':

Howto HDD and SSD Alignment
http://nlug.ml1.co.uk/2011/09/howto-hdd-and-ssd-alignment/608

(The above Reg article is now added into the links, thanks.)

Rather than use LVM or the old dos "MBR" partition scheme with "logical"
partitions, I'd recommend using the newer GPT partition scheme as
detailed there. The more recent versions of LVM are sympathetic to
sensibly aligning to specified boundaries. However, I don't know what
the LVM defaults do, anyone? Then again, why make life difficult to
calculate using LVM on top of a logical partition? With GPT you can
directly guaranteed the data alignment.

Or if using the old style MBR (due to an old BIOS), use no more than the
four primary partitions (do not use "secondary" or "logical").

A big help is to use ext4 with trim enabled (the "discard" mount option)
and to never go near 100% utilisation of the drive space.

"btrfs" is looking good but I've still a few questions about how it
treats SSDs...


Hope that helps a little.

Comments welcomed,

Cheers,
Martin


-- 
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Martin Lomas
martin at ml1.co.uk
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