Re: Current SSD setup recommendations for laptop with Debian
On Wed, 04 Jul 2012, Nick Lidakis wrote:
> > Once the OP asked about "alignment" I knew he needed a dose...
>
> I don't need a "dose", thank you. All my questions are valid and you did
Indeed, you don't need any dose of reality, and your questions are
valid. Any proper sysadmin knows of alignment, it is indeed important
and not just on SSDs.
Almost all of the relevant tools on Debian Wheezy (including the Wheezy
installer) automatically align partitions to 1MiB boundaries, which takes
care of almost every HDD and SSD block and erase-block alignment
requirements. USB "pendrives" are a different matter, and almost all of
those really want filesystems with heavy write access patterns that look
like the one for FAT filesystems.
LVM in Wheezy also knows to not botch AF (4KiB) alignment, but it might
not get erase-block alignment right should the erase-block be too large.
On good SSDs, it will not be too large and it will do the right thing
out of the box.
mdadm in Wheezy also does the right thing on most cases. When in doubt,
metadata format 1.0 preserves the host partition or device alignment, but it
has a severe drawback: on some RAID levels, component devices might looks
like a valid filesystem, so you risk the component device [as opposed to the
md raid device] getting mounted by mistake in some failure scenarios and
rescue-attempt scenarios.
> I'm not a tweaker; I need to get work done on my laptop. Also, I need the
> drive to perform reliably for as long as possible. My data is important to me
> and I try to use my computer hardware for as long as possible --not
> subscribing to the idea of disposable consumerism that is prevalent today.
The choice of SSD will be really important, then. Get one with a _lot_
of spare area for defect management and background defragmentation, and
with firmware known to be of high quality at cleaning after itself when
left idle. The type of flash memory will also matter a lot, the
simplest type of MLC will die much sooner than any alternatives (but it
will be a lot cheaper, enough that it might make more sense to replace
the drive sooner than to get one that will last longer).
> TRIM support is included in the latest kernels and
> hdparm utility. Are you telling me that the kernel kernel devs included
> useless code that I should not bother with?
You will have to test, to see if the combination of your storage stack
and a particular SSD does well at online TRIM. Batch TRIM sort of
"always works well enough". Online TRIM requires one to drain the
request queue even if the SSD does it fast, so on a drive with lots of
spare area (or unused area) it is likely to not be the best choice for
performance.
BTW: Some SSD controllers depend on being able to compress data to work
well. Do not get a drive based on those controllers if you are going to use
any OS-level encryption.
--
"One disk to rule them all, One disk to find them. One disk to bring
them all and in the darkness grind them. In the Land of Redmond
where the shadows lie." -- The Silicon Valley Tarot
Henrique Holschuh
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