Re: Spare SSD anybody?

[David Kastrup]

Michael Hendry <address@hidden> writes:

>> On 1 Jun 2016, at 10:07, David Kastrup <address@hidden> wrote:
>> 
>> David Kastrup <address@hidden> writes:
>> 
>>> Hi,
>>> 
>>> my current development SSD, graciously donated by James, currently has
>>> the following readings:
>>> 
>>> Vendor Specific SMART Attributes with Thresholds:
>>> ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED
>>> RAW_VALUE
>>>  5 Reallocated_Sector_Ct 0x0033 099 099 --- Pre-fail Always - 13
>>>  9 Power_On_Hours 0x0032 094 094 --- Old_age Always - 25748
>> 
>> Ok, I might have been panicking because of all the lines with "Pre-fail"
>> and "Old_age" but they only indicate the _category_ of the respective
>> settings.  Sorry for that.
>> 
>> I'm still trying to figure out the readings as such though.  The
>> "documentation" including online is not much help.
>
>
> Surely an SSD is entirely Solid State, so can’t wear out in the way a
> mechanical device does.

Seriously?  <URL:https://en.wikipedia.org/wiki/Wear_leveling>.  Which is
why SSD drives are great for servers and are put through the mills as
swap drive.

> Eventually, I suppose, even solid state devices will fail, but I doubt
> that SMART monitoring will give you advance warning of this.

It can keep track of the individual block wear pretty well, and the
average number of reliable block erasures is also known.  So failures
are not _exceptional_ but predictable.  So storage deterioration is
predictable as well as monitorable (either CRC errors or uncleared bits
directly after erasure).  You can get a hint about the bearings of a
rotating disk by monitoring its spinup (and noticing irregularities in
operation) but actual failures tend to come suddenly as platter damage
affecting an area.

-- 
David Kastrup