Re: SSD TBW

On 8/21/26 20:13, Cóilín Nioclásín Glostéir wrote:
> Lawrence D’Oliveiro <[email protected]> wrote:
> |----------------------------------------------------------------------|
> |"I found out that a common measure of the projected life of an SSD is |
> |being given in units of “terabytes written” (TBW). This will typically|
> |be much larger than the capacity of the drive itself, because it      |
> |includes the sum total of all write operations on the drive, including|
> |deletion of data.                                                     |
> |                                                                      |
> |For example, a 1-terabyte drive could have an expected figure of      |
> |merit, by this measure, of 1000TBW -- that means it should be able to |
> |endure a total of a petabyte (1000 terabytes) written to it before    |
> |showing signs of failure.                                             |
> |                                                                      |
> |But it seems to me, a 2-terabyte drive made of parts with the same    |
> |quality, meaning each storage cell has the same expected endurance as |
> |before, should have a proportionately greater figure of merit, namely |
> |2000TBW.                                                              |
> |                                                                      |
> |But the bigger drive will likely not last longer than the smaller one |
> |-- unless you don’t actually make use of the extra space.             |
> |                                                                      |
> |So why not divide the TBW by the actual capacity of the drive? Then   |
> |you end up with a ratio of how much can be written in total, to the   |
> |drive capacity -- call it, say, the “cumulative write ratio”. Both    |
> |those drives would have a cumulative write ratio of 1000.             |
> |                                                                      |
> |That number, it seems to me, correlates better to the overall quality |
> |of the unit than TBW does. E.g. if you see a bigger drive with a      |
> |smaller cumulative write ratio, you can suspect that they are cutting |
> |corners somewhere to keep the cost down."                             |
> |----------------------------------------------------------------------|
> 
> I do not yet have a first-hand experience of an SSD failure. Don Y

Bit late to this thread, but as ssd started to become more
affordable, started replacing all the mech drives with ssd.
Had a couple of failures, but never buy new. Run zfs file
system, which allows recovery from one or even two single
disk failures, depending on initial setup. For root drives,
run zfs mirrored root, which is an install option with
FreeBSD. Much faster than spinning drives, lower power
consumption, and worth it, just for those reasons alone.

Some systems here have been upgraded with sas interface
controllers. That allows the use of ex corporate ssds,
which tend to have a much better spec than some of the
consumer quality drives. Some of the Samsung sas drives,
for example, guarantee a full disk write and read every
day for five years or more, without failure. That's
effectively 100% reliable, under the lightly loaded
conditions here.

Ebay is a great source, and purchases here include a
batch of 17 sas 3840 Gb drives, marked as end of life,
but smartcontrol shows 9% wear, which is irrelevant here.
Several in a zfs pool for a few years, without a single
failure. Another was a disk array with 24 x 800Gb Samsumg
ssd. 520 byte sector size, but trivial to reformat to
512. 120 ukp delivered. More storage than i'll ever need,
most likely.

Sata drives not too bad either, a couple of failures
over the years,, but nothing serious. The real problem
is when such drives use a sata to usb converter, where
all bets are off worst case, and can even end up
completely bricking the drive. Still, they get cheaper
all the time.

The worst culprits are ssd memory sticks, some of
which wont even take a large file, ~5Gb write in
one go, without failure.

Chris

> complains in news:sci.electronics.design that an SSD suddenly
> completely failed, instead of gradual partial degradations of a hard
> disk. What does Lawrence D’Oliveiro mean by
> "before
> showing signs of failure."?
> This quotation gave me the impression that Lawrence D’Oliveiro does
> not expect the dramatic all-or-nothing scenario that Don Y reported.
> 
> This is a crosspost to news:sci.electronics.design
> (S. HTTP://Gloucester.Insomnia247.NL/ fuer Kontaktdaten!)