Your description of what your small Sandisk did matches exactly what you would expect if you had failed to overprovisioned it. Moving the data to the 240 Gbyte SSD just made more blocks available to be erased, but if you fill that disk up and you have not overprovisioned it, the same problem will happen again.
Its up to about 5 gigs free on the intel and its running sweet as with no problems. I always assumes that the 120 instead of 128 and 240 instead of 256, and 960 instead of 1TB was because they overprovisioned the flash on the drive so that the advertised capacity was able to be used correctly. If thats not the case then IMO they're lying about capacity on the sticker. All the other drives I have (samsung, really old seagate ones and intels) work perfectly at their capacity, its just both the small sandisk cheapies I have used which have suffered from this. Even after freeing up space they were aweful.
Your description of what your small Sandisk did matches exactly what you would expect if you had failed to overprovisioned it. Moving the data to the 240 Gbyte SSD just made more blocks available to be erased, but if you fill that disk up and you have not overprovisioned it, the same problem will happen again.
Its up to about 5 gigs free on the intel and its running sweet as with no problems. I always assumes that the 120 instead of 128 and 240 instead of 256, and 960 instead of 1TB was because they overprovisioned the flash on the drive so that the advertised capacity was able to be used correctly. If thats not the case then IMO they're lying about capacity on the sticker. All the other drives I have (samsung, really old seagate ones and intels) work perfectly at their capacity, its just both the small sandisk cheapies I have used which have suffered from this. Even after freeing up space they were aweful.
I am not at all sure that SSDs are actually created with a binary multiple of data blocks. I initially thought like you that a 120 Gbyte drive might actually have 8 Gbytes hidden, but I have seen no evidence of that. My guess now is that the die actually has 120 Gbytes of SSD. If there is extra space, my guess is that it is used for the microcontroller and RAM to operate the SSD, plus possibly some fast non-volatile blocks of storage (not flash) to be used as cache. SSDs do not fall in heap if the power goes off while a write is in progress - they do not seem to lose the data. So there must be some fast non-volatile storage to make that possible, or a method of keeping enough power available for a write to complete after the power is lost. Older SSDs tended to have the controller on a separate chip or separate die, but I am not sure how it is done now. It would likely be cheaper to have all that on the same die as the flash storage.
I do know that all the SSDs I have came with software from the manufacturer that had overprovisioning as part of the initialisation process. And they all recommend at least 10% overprovisioning. They would not do that if there was sufficient hidden overprovisioning. Yes, that could cause problems with advertising the size when you really can not use the full size and get decent performance. But SSDs seem to have been like this since they were first sold, so most people understand that they do not get to use 100% of the storage. The thing about overprovisioning is that the correct amount depends on how you are using your SSD. If you are frequently writing 100 Gbyte files to one, you need more than 100 Gbytes of overprovisioning. If you are only ever using it for a transactional database where the largest updates are a few megabytes and the daily total of writes is less than a gigabyte, then you might choose to use much smaller overprovisioning. You can not make those choices if the manufacturer has made the decision to provide some generic amount of overprovisioning.
Are you subscribed to our RSS feed? You can download the latest headlines and summaries from our stories directly
to your computer or smartphone by using a feed reader.
Trusted
