On Wed, 23 Jan 2008, Guy Rouillier wrote:
Flash has a limited number of writes before it becomes unreliable. On good quality consumer grade, that's about 300,000 writes, while on industrial grade it's about 10 times that.
The main advance that's made SSD practical given the write cycle limitation is increasing sophisticated wear leveling: http://en.wikipedia.org/wiki/Wear_levelling
The best devices now use static wear levelling; overviews at http://en.wikipedia.org/wiki/Static_Wear_Leveling and http://www.storagesearch.com/siliconsys-art1.html
The basic idea is that the number of writes to each block is tracked, and as it approaches the limit that block gets swapped with one that has been more read-only. So essentially the number of writes before failure approaches something closer to 1M x number of blocks. This means that as the size of the device goes up, so does its longevity. If you believe the hype, the combination in the increase in size of designs with these more sophisticated wear-levelling approaches has now crossed the line where it's more likely a standard moving-parts hard drive will fail first if you compare it to a similarly sized SDD doing the same job (a standard mechanical drive under heavy write load also wears out faster than one doing less work).
-- * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
