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From Toke Eskildsen ...@statsbiblioteket.dk>
Subject Re: SSD Experience (on developer machine)
Date Fri, 26 Aug 2011 08:13:14 GMT
On Wed, 2011-08-24 at 13:42 +0200, Federico Fissore wrote:
> I add a question. Toke you said that "the current state of wear can be 
> queried". How?

With a S.M.A.R.T.-tool, preferably up-to-date to get it to display the
vendor-specific properties in an easy to understand manner.

On my Ubuntu-box with a 160GB Intel X25-M G2, 
sudo smartctl -A /dev/sdb1
gives me (abbreviated by me)
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE
UPDATED  WHEN_FAILED RAW_VALUE
  9 Power_On_Hours          [...]   9372
 12 Power_Cycle_Count       [...]     50
225 Host_Writes_Count       [...] 176888
233 Media_Wearout_Indicator [...]      0
and 
http://forums.storagereview.com/index.php/topic/28649-intel-x25-interpreting-smart-values/
tells me that I'll have to divide the raw value from #225 with 29,8,
resulting in 5,8TB written in total (about 15GB/day).

Some vendors provide specific software that makes it much easier.
Intel makes the Intels SSD Toolbox that unfortunately is Windows only.

> AFAIK, cells target for a write are chosen just randomly between the 
> free ones, ignoring other factors

That would be a very bad wear-leveling strategy. Keeping a counter for
each cell and selecting the free cell with the lowest count is trivial.
However, given the bumpy road to great SSDs, I am sure that some vendors
has done it this way.

Regards,
Toke Eskildsen


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