[CentOS] SSD Drives

Thu Feb 2 22:19:06 UTC 2012
Peter A <loony at loonybin.org>

On 02/02/12 17:01, William Warren wrote:
> On 2/2/2012 2:15 PM, Peter A wrote:
>> If you're worried about io reliability, then buy a (way more expensive)
>> SLC drive, rather than the consumer level MLC... We have some SLC drives
>> here that from their manufacturer have been rated at 3 or more years of
>> 100% write 24x7...
>> Peter.
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> exactly hence why i said stay with OCZ or Intel..MLC drives are the
> best.  But also the smaller the process node the shorter the lifespan of
> the flash.  MLC drives will also over provision more spare flash area
> most times.
Aeh... that's exactly the opposite of what I said. MLC (multi level 
cell) SSDs store more than one bit per cell. In current devices that's 
mostly 2 bits per cell, but more is around the corner. On an SLC (single 
level cell) there is only one bit per cell - true binary just like what 
we have in RAM and others. SLC devices are superior in reliability 
because it simply takes a lot more disturbing of a cell to make it lose 
enough charge that a 1 gets interpreted as a 0. The devices are also 
usually faster, especially on a re-write basis.
A Oracle 96GB flash card (SLC) physically has 128GB. Most consumer MLC 
devices with 128GB are sold as 120GB visible... Again in favor of the 
SLC. Only problem is that you pay for what you get. SLC devices are 
significantly more expensive. Fusion I/O and all the other server ssd 
vendors do the same - they give you a cheap MLC device with limited 
performance and reliability and a high end, much more pricey SLC unit.