Someone asked how long I expected my SSDs to last. The context was
swapping to SSD, but obviously it actually depends on the usage
pattern as a whole, not just one aspect of it. Here’s the SMART
attribute data for an Intel SSD that’s been in constant light usage,
including swapping, for the last 18 months:
smartctl 5.40 2010-07-12 r3124 [i686-pc-linux-gnu] (local build)
Copyright (C) 2002-10 by Bruce Allen, http://smartmontools.sourceforge.net
=== START OF READ SMART DATA SECTION ===
SMART Attributes Data Structure revision number: 5
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE
3 Spin_Up_Time 0x0020 100 100 000 Old_age Offline - 0
4 Start_Stop_Count 0x0030 100 100 000 Old_age Offline - 0
5 Reallocated_Sector_Ct 0x0032 100 100 000 Old_age Always - 0
9 Power_On_Hours 0x0032 100 100 000 Old_age Always - 12131
12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 19
192 Power-Off_Retract_Count 0x0032 100 100 000 Old_age Always - 5
225 Load_Cycle_Count 0x0030 200 200 000 Old_age Offline - 9248
226 Load-in_Time 0x0032 100 100 000 Old_age Always - 16301
227 Torq-amp_Count 0x0032 100 100 000 Old_age Always - 1
228 Power-off_Retract_Count 0x0032 100 100 000 Old_age Always - 1018723636
232 Available_Reservd_Space 0x0033 100 100 010 Pre-fail Always - 0
233 Media_Wearout_Indicator 0x0032 099 099 000 Old_age Always - 0
184 End-to-End_Error 0x0033 100 100 099 Pre-fail Always - 0
A couple of caveats about interpretation. Firstly, TYPE
is the type of the attribute, not a commentary on its current value -
i.e. the ones that say Old_age will still say that on a brand
new device and Pre-fail doesn’t mean a failure is imminent.
Secondly high VALUE fields are better: they mostly start at a
high value (here, mostly 100) and decline as things get worse.
Anyway Media_Wearout_Indicator is the one of interest
here. Intel describe this as follows:
The E9 SMART attribute reports a
normalized value of 100 (when the SSD is brand new out of the factory)
and declines to a minimum value of 1.
The normalized value decreases as the NAND
erase cycles increase from 0 to the maximum-rated cycles. Once the
normalized value reaches 1, the number will not decrease, although it
is likely that additional wear can be put on the device.
So the current value means the device has performed at least 1% and
less than 2% of the maximum rated erase cycles; if current usage
patterns persist it’d take between 75 and 150 years to reach the
maximum.
Obviously this isn’t the whole story. The device only has a three
year warranty, and plenty of other things could go wrong either with
the disk or the computer containing it; and Intel could have got their
sums wrong. Nevertheless I’m pretty comfortable that flash wear is
not going to be a problem in the near future.