Theoretically all sectors in over provision are erased - practically they are either erased or waiting to be erased or broken. What you have to understand is that sectors on SSD are not where you really think they are - they can swap place with sectors with over provisioning are, they can swap place with each other ect … stuff you see as a disk from 0 to MAX does not have to be arranged in sequence on SSD (and mostly never is) If you never trim - when your device is 100% full - you need to start overwrite data to keep writing - this is where over provisioning shines: ssd fakes that you write to a sector while really you write to a sector in over provisioning area and those magically swap places without you knowing -> the sector that was occupied ends up in over provisioning pool and SSD hardware performs a slow errase on it to make it free for the future. This mechanism is simple, and transparent for users -> you don’t know that it happens and SSD does all heavy lifting. Over provisioned area does have more uses than that. For example if you have a 1TB drive where you store 500GB of data that you never modify -> SSD will copy part of that data to over provisioned area -> free sectors that were unwritten for a while -> free sectors that were continuously hammered by writes and write a static data there. This mechanism is wear levelling - it means that SSD internals make sure that sectors on SSD have an equal use over time. Despite of some thinking that it’s pointless imagine situation where you’ve got a 1TB drive with 1GB free and you keep writing and modifying data in this 1GB free … those sectors will quickly die due to short flash life expectancy ( some as short as 1k erases !!!!! ). So again, buy a good quality drives (not a hardcore enterprise drives, just good customer ones) and leave stuff to a drive + use OS that gives you trim and you should be golden !!!! > On 15 May 2017, at 00:01, Imran Geriskovan <imran.geriskovan@xxxxxxxxx> wrote: > > On 5/14/17, Tomasz Kusmierz <tom.kusmierz@xxxxxxxxx> wrote: >> In terms of over provisioning of SSD it’s a give and take relationship … on >> good drive there is enough over provisioning to allow a normal operation on >> systems without TRIM … now if you would use a 1TB drive daily without TRIM >> and have only 30GB stored on it you will have fantastic performance but if >> you will want to store 500GB at roughly 200GB you will hit a brick wall and >> you writes will slow dow to megabytes / s … this is symptom of drive running >> out of over provisioning space … > > What exactly happens on a non-trimmed drive? > Does it begin to forge certain erase-blocks? If so > which are those? What happens when you never > trim and continue dumping data on it? -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
