3 ms·

>or double the ECC bits Are you aware of even a single ssd product allowing user to reconfigure capacity outside of obtaining secret/proprietary non public man

by rasz 4y ago

>or double the ECC bits Are you aware of even a single ssd product allowing user to reconfigure capacity outside of obtaining secret/proprietary non public manufacturer service software? The only technical way for a drive to automagically shrink size on its own is by starting to mark TRIM freed sectors as BAD and hoping OS running on top will be able to recognize this and transfer BAD status to the filesystem - thats a lot of assumptions. No such drive exists either, drives ship with spare capacity and existence of BAD sectors is treated as a catastrophic event signaling running out of backup NAND.

consp 4y ago
On SAS disks you can reduce the capacity. I don't know if this has any influence on spare sectors and write cycles though.
- rasz 4y ago
  You can reserve space by setting host protected area (HPA). There are even people theorizing this might add provisioning are to an SSD https://www.thomas-krenn.com/en/wiki/SSD_Over-provisioning_using_hdparm https://www.thomas-krenn.com/en/wiki/SSD_Over-provisioning_u... . But so far there is zero evidence for it. HPA is not a magic nobody touches area, its an area reserved for special superuser use and no Drive will simply start reusing it for its own internal processes.
londons_explore 4y ago
Drives internally do this with their reserved sectors. They also reallocate sectors between 'fast access' and 'long term storage', where the long term storage uses larger logical pages and hierarchical ECC, allowing a lower percentage of ECC overhead at the cost of performance. At some point, I wouldn't be surprised if an SSD manufacturer releases a drive with a driver which can reduce the user-visible disk size as it ages. It would probably involve using a 'balloon file', in a similar way to Memory ballooning [1] [1]: https://en.wikipedia.org/wiki/Memory_ballooning https://en.wikipedia.org/wiki/Memory_ballooning
jasomill 4y ago
You can use hdparm(8)'s --dco-setmax option to reduce the visible size of most SATA drives. This is not particularly useful for single drives — leaving unpartitioned space works just as well, assuming an OS that never writes to it — but it does stop TRIM-ignorant RAID controllers from potentially kneecapping SSD GC by "initializing" intentionally unused space. Though I imagine most RAID controllers initialize with zeroes, and I hope SSD firmware doesn't reserve flash to store large extents of zeroed sectors, so this shouldn't be terribly useful for underprovisioning purposes. But without extensive testing or access to SSD firmware algorithms, it's hard to say.
- rasz 4y ago
  This is one layer too high - ssd firmware has no way of knowing your intentions purely from filesystem/sector activity.
fomine3 4y ago
Intel SSD DC series https://www.ioncomputer.com/ion/body/documents/over-provisioning-nand-based-ssds-better-endurance-whitepaper.pdf https://www.ioncomputer.com/ion/body/documents/over-provisio...

by rasz 4y ago

consp 4y ago

On SAS disks you can reduce the capacity. I don't know if this has any influence on spare sectors and write cycles though.

rasz 4y ago
You can reserve space by setting host protected area (HPA). There are even people theorizing this might add provisioning are to an SSD https://www.thomas-krenn.com/en/wiki/SSD_Over-provisioning_using_hdparm https://www.thomas-krenn.com/en/wiki/SSD_Over-provisioning_u... . But so far there is zero evidence for it. HPA is not a magic nobody touches area, its an area reserved for special superuser use and no Drive will simply start reusing it for its own internal processes.

londons_explore 4y ago

Drives internally do this with their reserved sectors. They also reallocate sectors between 'fast access' and 'long term storage', where the long term storage uses larger logical pages and hierarchical ECC, allowing a lower percentage of ECC overhead at the cost of performance. At some point, I wouldn't be surprised if an SSD manufacturer releases a drive with a driver which can reduce the user-visible disk size as it ages. It would probably involve using a 'balloon file', in a similar way to Memory ballooning [1] [1]: https://en.wikipedia.org/wiki/Memory_ballooning https://en.wikipedia.org/wiki/Memory_ballooning

jasomill 4y ago

You can use hdparm(8)'s --dco-setmax option to reduce the visible size of most SATA drives. This is not particularly useful for single drives — leaving unpartitioned space works just as well, assuming an OS that never writes to it — but it does stop TRIM-ignorant RAID controllers from potentially kneecapping SSD GC by "initializing" intentionally unused space. Though I imagine most RAID controllers initialize with zeroes, and I hope SSD firmware doesn't reserve flash to store large extents of zeroed sectors, so this shouldn't be terribly useful for underprovisioning purposes. But without extensive testing or access to SSD firmware algorithms, it's hard to say.

rasz 4y ago
This is one layer too high - ssd firmware has no way of knowing your intentions purely from filesystem/sector activity.

fomine3 4y ago

Intel SSD DC series https://www.ioncomputer.com/ion/body/documents/over-provisioning-nand-based-ssds-better-endurance-whitepaper.pdf https://www.ioncomputer.com/ion/body/documents/over-provisio...