[GTALUG] nvme SSD: critical medium error, dev nvme0n1

[D. Hugh Redelmeier]

| From: Stewart C. Russell via talk <talk at gtalug.org>


| Drive is a 2+ year old Intel 512 GB SSD.
|     data_units_read                     : 10,349,479
|     data_units_written                  : 10,098,299

I wonder what a unit is.  A logical sector (512 or 4096 bytes)?

The ratio of those numbers surprises me.  I've always assumed that
reads are more common than writes.  Except for archiving.  Those
numbers are so very very close

|     host_read_commands                  : 183,018,841
|     host_write_commands                 : 136,702,227

These numbers are quite close but
(a) not as close as the previous pair
(b) larger than the previous pair (how could that be?)

|     unsafe_shutdowns                    : 10

There's a chance that this number explains your bad data.  

|     media_errors                        : 803
|     num_err_log_entries                 : 844

You can read this log (using smartctl).
Only the most recent N entries might be preserved.

| * what I should be looking for in stats (nvme smart-log-add doesn't give
| me anything at all, so no wear-levelling stats)
| 
| * a decent brand to replace it with. I'm likely okay with a SATA SSD.

I know too little to answer this.  There are lots of review sites (of
varying quality).

You want an NVMe drive, right?

Some of the inexpensive NVMe drives "borrow" some RAM from your main
memory.  That may be a Good Thing (cheaply increasing performance) or
not (adding a new and exciting way that a system crash could curdle
your disk).

There are a lot of sins that can be covered up by firmware.

Here's one:

SLC > MLC > TLC > QLC
 1     2     3     4	bits per cell

The more bits per cell, 
- the more bits you can fit on a flash chip
- the slower the operations
- the sooner the cell will wear out.

For consumers, SLC hasn't ever been available.
MLC is probably gone from the market
TLC is very common
QLC is just coming in.

Many drives reserve a bit of flash to use in SLC mode as a fast
buffer.