On 18/10/16 13:24, John Rumm wrote:
On 17/10/2016 21:30, The Natural Philosopher wrote:
On 17/10/16 20:07, John Rumm wrote:
On 17/10/2016 12:34, The Natural Philosopher wrote:
On 17/10/16 11:31, John Rumm wrote:
It makes far more sense to ensure the partitions are aligned so that
the
OS allocation unit is on a 4K boundary (which is the default action
on a
modern OS anyway)
My point is that that is what the SSD firmware will in fact do.
No matter where the partition boundary is.
Could you provide a link to a manufacturers documentation for this since
I have not yet seen any SSDs that claim to be able to remap misaligned
partitions?
There are no 'misaligned' partitions.
Just partitions.
OK, so if you look at the Intel document from 2014[1], they explain why
misaligned partitions cause performance impacts on their drives of that
time. You have claimed that that information is out of date, and its no
longer an issue. Could you point to an authoritative source that
justifies that claim?
Or are you claiming that Intel drives are just way behind the current
state of the art, and other makers drives don't suffer the problem, but
then Intel ones still do? In which case it sounds like a strong
marketing hook the other drive makers would use. Could you point to
some documentation reflecting this?
If you look at the actual strategies - and I supplied pointers to then -
google 'wear levelling' you will realise that is a massively complex
process right away, and completely destroys any relationship between
what the disk reports as a block device and where physically the data is
stored. Yea even unto splitting blocks of data up into different flash
pages or amalgamating two different 'sectors'; into one flash page.
IN essence the disk is a database, with sectors located wherever they
happen to end up, and indexed by a database like structure that relates
the sector number of the logical device, to an offset in a flash page
somewhere on the disk.
And tuning the garbage correction and read and write algorithms is the
best way to increase the system life.
Logical sectors that have never been written , simply do not have any
physical area assigned to them.
The asertion of the partitioneers, is that if you start a partition with
whatever information it has in it, on a less rthan e.g. 4K boundary,
that will result in more cross-page writes. Firstly I dont see that is
true even if the algorithm is always to apply aligned sectors in 4k
chunks to a 4k flash page.
But I see no reason why if the disk detects a sequence of data starting
at say 133rd sector....it would not start that at the beginning of the
flash page, assuming it has no prior knowledge of this sequence.
After all, all that is being maintained is a database of Logical
sector-physical flash page
age offset.
There is no reason to say that because the sector number is, modulo 4,
number 3, that the page offset should also be 3.
Note that nearly all of this IIRC only applies to windows, as Linux file
systems are aligned on much larger page sizes anyway.
The point I wanted to make way back before all the name calling started,
was that they way data is physically organised on a flash disk bears no
relation whatsoever to how it is presented logically. It is organised
precisely to minimise writes and erases, and to ensure that when those
take place, they are as evenly spread as possible.
Therefore theories that changing the nature of OS access to the
*logical* structure will impact on the physical processes are at best
optimistic simplistic and dependent on a poor implementation of wear
levelling and garbage collection algorithms. At worst they are risible
nonsense.
And there is evidence that more than one manufacturer has firmware that
exactly understands partitions of the NTFS sort and has adjusted its
algorithms accordingly. Why would they not?
https://en.wikipedia.org/wiki/Write_...age_collection
A little knowledge is a dangerous thing., To someone with a little
knowledge, someone with a lot more appears ignorant and uninformed.
The 'partition your SSD correctly' appears to be an urban (windows)
myth, that has propagated widely, and yet no explanation of why it works
is consistent with my understanding of how logical to physical mapping
works in a real life SSD.
And because I have written code to analyse and understand file systems
at the sector level, I know its really not hard to understand what type
of FS and what structure is located where, on a disk.
The crucial step is of course coding that can cope with arbitrary
locations of a 512 byte sector, rather than a 4k or 16k block that it
might be part of.
I can conceive that a rubbish programmer with no understanding of file
systems or flash might cobble up something that bad for a prototype
product, but in a fiercely competitive field with longevity being an
essential part of the product attributes, its unlikely that better
algorithms and more flexible mapping systems would not evolve.
[1]
http://www.intel.co.uk/content/dam/w...tech-brief.pdf
Is an interesting document to be sure.
I cam also point you at documentation by quite large companies showing
how to reduce your carbon emissions with windmills, and how seroxat is a
wonder drug with no side effects.
My best guess is that someone challenged Intel with some urban myth, and
some nerd got tasked to write some 'support literature' to 'take care of
it' from a marketing POV, the technical solution already having moved on...
But even if its in fact true, it is so for only one make of drive at one
particular time. As I said. tuning the firmware is big business and
means lots of dollars. There are half a dozen or more people who own and
sell firmware and SSD controller chipsets to manage SSDS.
Who knows WHAT goes in inside?
Pretty much only the people who wrote the firmware, in detail BUT the
flow of product information and PHd papers shows which way the wind is
blowing an the general classes of solutions. See the wiki article on
wear levelling.
PS for those paranoid about security, note that writing zeros to every
sector on an SSD disk does not begin to guarantee the erasure of ANY
data on the chip at all.
Now should we talk about internal data compression...;-)?
--
Microsoft : the best reason to go to Linux that ever existed.