> Sad how a simple "battery" is not included in such devices, so maybe
> low-power DRAM could be used for faster writes and longer lifetimes.

Batteries are usually limited to high-end products. Also, DRAM
uses quite a bit of electricity, so the battery would be more
for "swapping" the contents to flash while power is not there.

> With hard disks, one just "uses them", with no need or worry

Harddisks also come in variants for 24/7 use and those for PC.

> But knowing how manufacturers make such disks last EXACTLY
> their "warranty period", I really doubt it!

I also doubt that they would last that long if HEAVILY used,
maybe just okay for the manufacturers to replace those which
are used more than predicted and thus break during warranty.

>> if you use a FLASH based device in an environment with lots of writes
>> then you expect to be replacing it on an accelerated schedule.

The "lots" should probably be "LOTS" there: As mentioned earlier
in this thread, SSD already ship with extra capacity. They keep
track how often which area is used and just use fresh areas when
they predict or sense some area to be over-used. Different from
harddisks, over-used areas are not lost for reads but for writes
so data is normally never lost, just the capacity decreases. As
the SSD initially has much more capacity than visible for users,
it can keep working perfectly from the user perspective for very
long time even at relatively heavy use. We even use SSD for some
database servers, which of course have backups outside SSD, but
I think those SSDs will still live much longer than needed and we
will replace it when we run out of space, much before it breaks.

Also, the sweet spot for SSD sizes, price wise, is 60 to 500 GB
at the moment, much closer to 1 Euro per GB than to two. For the
more freedos4kids like sizes, you can still get 8 GB SATA SSD for
15-30, while you would only get 1 or at most 2 GB IDE DOM for the
same price. There are also not that many IDE SSD, but I saw a 16
GB one for 25 Euro with 40 pin ZIF connector (for subnotebooks?).

So as you can imagine, the big market for SSD today is SATA, with
some extra models designed directly as PCIe cards because that is
potentially faster than SATA depending on your SATA controller...
You can get SSD in sizes of up to circa 1 TB, but of course at 1
Euro per GB that cannot be compared to harddisks where you will
easily pay less than 1 Euro for 10 gigabytes today even for some
modern small and power efficient 2.5 inch models.

USB sticks are a completely different story - they are commodity
stuff today, when people run out of space or a stick breaks, they
just buy the next stick, so there should be lower quality, speed
and wear-leveling compared to SSD, also because most users only
access their USB sticks occasionally and do not use it as disk.

> NOT concerned about absolute speed (not with UIDE, anyway!)

With the sizes of UIDE that you run, you could actually boot from
DVD and then use a RAMDISK, which big UIDE caches are similar to.

> nor power consumption

SSD are similar in power consumption to 2.5 inch harddisks, but as
they do not spin, they can enter and leave idle mode very quickly,
so they can easily be idle much more than a conventional harddisk.

> but I AM still "concerned" over all noted in this thread
> re: FLASH-disk "cycle limits"!

There seem to be some notorious SSD models which just break down
completely, but as far as I could tell, none of those was due to
exhausted flash write cycles. It rather seems to be weak firmware
(we both know that firmware is no quality market today) which is
likely to get stuck in unrecoverable data status when you power
down or crash the PC in unexpected ways too often. Such "bricked"
drives apparently need at least formatting to recover, although
some can be debugged/fixed with special "serial console" cables.

I checked some estimates online - even when you always fill the
whole SSD at max speed, not taking time to read any data, usual
sizes and speeds of SSD still mean that it takes years to wear
out the cells themselves thanks to over-capacity and wear-level,
and typical warranty periods reflect that. Consumer SSD seem to
be designed for less intense access but again, if you do not
overwrite, defrag, wipe or similar your whole disk all the time,
you will write to much smaller areas than you read.

Apparently 2- or 3-bit, especially high-density MLC flash can
handle 1k-10k write cycles, but high end SLC is more like 100k
cycles but at a much higher price, often server products. The
MLC based consumer SSD have 10s of percents of extra capacity
internally to be able to replace worn out cells automatically.

Wikipedia: floating-gate NOR flash can even achieve 1M writes
SLC (single level cell) and still 100k MLC (multi level cell)
but only CF used to use NOR flash, NAND flash is much smaller
and USB sticks, SD cards and similar use it, as do most SSD to
fit really large amounts of storage into common 2.5in housings.

Also, Wikipedia says old NOR CF cards still were only rated at
10k writes, while new NAND CF cards are rated 1M, I guess due
to now also using wear-levelling and over-size? I do not think
they would put EXTREMELY high quality flash chips in CF cards.

Again, even only 1000 writes for a 120 GB SSD are 120 TB data
to be WRITTEN. Takes 2 weeks at 100 MB per second non-stop but
MANY months in a normal desktop PC used for normal work... :-)

Regards, Eric

RSA(R) Conference 2012
Save $700 by Nov 18
Register now
Freedos-user mailing list

Reply via email to