M550: how to see a total number of bytes written

[AKazak]

Greetings, dear community!

  I am thinking of purchasing a second-hand M550 SSD drive of 1 TB.

  How do I check a total number of bytes ever written to the SSD?

Thank you for the prompt advice.

[targetbsp]

If you're concerned over wear, number of bytes written is irrelevant.  The wear is measured by SMART attribute CA.  You can check the SMART data using Crystal Disk Info which will also nicely show the life left as a percentage in a big coloured box in the top left.

[AKazak]

Thank you.

Can you share a screenshot showing the CA and graphic indicator please?

[targetbsp]

This review has one: http://www.technologyx.com/featured/crucial-m550-ssd-512gb-review/3/

[AKazak]

OK.

As far as I see from the screenshot Current CA = 100 and Worst CA = 100.

Does this mean that at the screenshot example the current CA is worst?

What is the best CA value (new SSD) and what is the worst value (dead SSD)?

[targetbsp · Accepted solution]

It counts down from 100 so that drive is new.

'Worst' for smart data indicates the worst value it has ever been.  Threshold indicates what you are thinking of as worst. Though Threshold is unused on the drives.

Also, wear is just a guideline to when the NAND may fail. You can't accurately predict wear anymore than you can predict how long a car will last from its mileage.  It might last much longer than indicated, it might not last that much.

[AKazak]

Everything is clear now.

Thank you.

[bogdan]

targetbsp is right that it is NAND wear that is important. 

But it is still possible to know total number of bytes written (by host system) to M550  You can use recent version of CrystalDiskInfo (it will show 'Total Host Writes' in the upper right part of the window or you can take the value of 'F6 Total Host Sector Writes' SMART attribute, convert it from hexadecimal to decimal (if necessary) and multiply by 512 bytes. That is what CrystalDiskInfo automatically calculates for you.

[AKazak]

Thank you.

Can you suggest an alternative to CrystalDisk Info for Mac OS please?

[targetbsp]

That's an approximation though (unless you always happen to have written multiples of 512 bytes?).  But since we've already mentioned that all of this wear measuring is more or less a guess anyway, I don't spose it much matters.