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This content follows the TrueNAS CORE 13.0 releases. Use the Product and Version selectors above to view content specific to different TrueNAS software or major version.
SLOG Overprovisioning
2 minute read.
Last Modified 2023-08-22 16:12 EDTOver-provisioning SLOG SSDs is useful for different scenarios. The most useful benefit of over-provisioning is greatly extending SSD life. Over-provisioning an SSD distributes the total number of writes and erases across more flash blocks on the drive.
Seagate provides a thoughtful investigation into over-provisioning SSDs here: https://www.seagate.com/blog/ssd-over-provisioning-benefits-master-ti/.
Some SATA devices are limited to one resize per power cycle. Some BIOS can block resize during boot and require a live power cycle.
To over provision a SLOG device, log in to TrueNAS and go to System > Advanced. Enter an over-provision value corresponding to the new size in GB in the Log (Write Cache) Overprovision Size in GiB field.
When this value is applied, the over-provision value is applied whenever a pool is created with a SLOG device.
It is impossible to restore an over-provisioned SLOG device back to original capacity without running command disk_resize after first destroying the pool it was part of and issuing a full power cycle.
Only one over-provision/under-provision operation occurs per power cycle.
Erasing the over-provision setting in System > Advanced Log (Write Cache) Overprovision Size in GiB field and setting to none prevents future SLOG devices from being over-provisioned.