[clug] SSD drives and lots of writes

Steve McInerney steve at stedee.id.au
Mon Sep 24 00:31:51 MDT 2012

Ahh this sounds like cargo culting of "accepted wisdom" from the early days of 

1. "shorter" is subjective:
So how long is long? To help users estimate how long an SSD will last, SSD 
vendors such as OCZ have come up with formula: a drive's life span equals its 
capacity multiplied by its write endurance rating, divided by the average 
daily writes. For example, the 120GB Vertex 3 SSD has a write endurance rating 
of 3,000 cycles. If you write 50GB on the drive daily, the total number of 
days the drive will last before becoming unreliable is: (120 x 3,000)/50 = 
7,200 days, which is about 20 years. If you write an average of 100GB a day, 
the drive would last about 10 years.

If you're still using a magnetic disk after 10 years, more power and risk to 
you, let alone an SSD. :-)

More seriously, in 10 years, where would we expect the size of then current 
SSD's to be? 2002, they were around... 60Gb?
vs 1-2Tb 10 years later.
I'd be expecting to see 1-3Tb SSD's as being "common" buys in 10 years time.

So ignoring the "shortened" lifespan, I'd suggest that by the end of life of 
the disk you'll be laughing how you ever managed to fit anything on the thing 
in the first place.

2. Windows and it's pagefile.
If lots of writes killed a drive, then the net would be *full* of advice for 
folks to move their windows pagefile.sys off the SSD; my googlefu suggests 
it's the exact opposite.

Personally, skip the asking for thoughts; go and google for the facts. :-)

- Steve

On 24/09/12 16:08, Kim Holburn wrote:
> I like my Macbook air.  I like it because it's light, fast, stable and runs
> unix.  I hate that Apple has soldered the memory to the board so you can't
> change it and I'm not so happy the direction they're going with their GUI.
> But even if it has limited memory, it has an SSD drive which means you can
> run lots of applications and it pages very fast because of the SSD.
> This gave me the idea of running my linux system at home with an SSD system
> disk.  SSD disks big enough to hold a system are not that expensive
> anymore.
> I mentioned it to someone at my work and they said: don't put /var/log on
> the SSD because it will shorten the life with all that writing.  Oh I
> thought yes, SSDs have a limited number of writes, everyone knows that, but
> is it true?  And is it true that file systems really do write that often or
> do they cache the writes and write in a big bunch?  (Even if atime is on.)
> I noticed that the latest ubuntu has a default of mounting partitions with
> relatime which is similar to noatime.  Good.  If /var/log was bad then swap
> would be bad too.
> So I thought, perhaps I could get another smaller SSD drive, say 20GB or
> 30GB for swap (and maybe /var/log).  I could flog it with writes while my
> system disk was mostly just reads and would last a long time.  But is this
> all true?  What are your thoughts about whether modern SSD drives have
> their life shortened by lots of writes?
> Kim
> PS: my system boots tremendously fast from the SSD.

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