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Re: [OFF-LIST] Re: Measuring (or calculating) how many bytes are actually written to disk when I repeatedly save a file




Thanks to all who responded (even off list)!

I will respond to some of the other posts if they did something like ask a 
question.

I am exploring smartctl and sar (I found atsar for wheezy and loaded it, adn 
smartctl in smartmontools -- I had heard of (and even used smartctl sometime 
in the distant past but don't recall ever having heard of sar -- it looks 
useful but will require some man reading.)

On Saturday, April 06, 2019 04:01:14 PM Richard Owlett wrote:
> *BEWARE*
> I've replied offline because I've done some *HEAVY* handed editing.

Everybody should do heavy handed editing -- edit it down to what you are 
responding too.

If you edit appropriately, it is much more appropriate to reply to the list 
where your response (and the responders to your post) can help anybody / 
everybody -- I will send my response to the list.

(Aside: You surely don't need to use bold caps, either would be enough by 
itself.)

> I wanted to respond to specific details without causing chaos.
> i am *NO WAY* an expert authority
> 
> On 04/06/2019 12:39 PM, rhkramer@xxxxxxxxx wrote:
> > Background: I am considering buying a new disk but I know that,
> > at least often for SSD drives, they now specify what I will call the
> > longevity in terms of TB TBW (iiuc, that is terabytes total bytes
> > written).
> 
> Will the new disk be mechanical or SSD?

That is part of the decision I'm tryig to make.

> The references you refer to --
> Do they consider newer technologies referred to as "wear leveling"?

I didn't look for that, from other reading, my understanding is that "good" 
SSDs do wear leveling, that is how they obtain large TBW ratings when each 
cell (iiautrw (if I am using the right word)) has a rating of something like 
1000 write cycles.  (I mean, if you wrote to the same place 1000 times, you 
might wear it out, but by using wear leveling, you write the same (or some of 
the same) information to different parts of the disk.  You might write some 
files 10,000 times, but not to the same place, thus the 1000 writes don't wear 
out one spot.

> > Anyway, I edit large files many times a day and try to save it at
> > each edit or  partial edit (at a guess, one particular file is
> > around 100 MB, and I may save it 200 or more times a day).
> 
> 100 MB is *NOT* large.> 

It is if it is all my own text / prose.  (And, in any case, it is to me ;-)

> > [SNIP}
> > 
> > 2. A lot of my editing involves editing near the end of a file.  I
> > assume that the software that saves the file is smart enough not to
> > rewrite the entire file but instead to preserve the beginning of the
> > file and just rewrite the changed part of the file (or from there to
> > the end of the file).
> 
> As phrased, I doubt that is a safe assumption.
> 
> Before commenting
>     I assert I am *NOT* an expert ;/
> 
> 1. I suggest you describe what you are editing.
> 2. As 100MB is rather small, why not do total save with serial number as
> part of filename and once a day/week/month save data under different
> filename and then reuse previous data space.

I am not sure what that would accomplish (except requiring more work on my 
part).

> This is worth exactly what you paid for it ;/
> I'm satisfied if I provided food for thought.
> 
> *YMMV*