SLOG Over-Provisioning

Over-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/.

For more general information on SLOG disks, see SLOG Devices.

Some SATA devices are limited to one resize per power cycle. Some BIOS can block resize during boot and require a live power cycle.

For best stability and hardware compatibility, offline active SLOG SSDs before resizing for over-provisioning.

If the disk is assigned to an active pool, remove it from the pool. ZFS permits removing and re-adding SLOG disks to an active pool at any time.

1. Go to Storage and locate the pool with the SLOG drive assigned. Click Manage Devices on the Topology widget to open the Devices screen.

2. Select the target disk under Log. Click Offline on the ZFS Info widget. Confirm and click Offline in the Offline Disk dialog to offline the disk.

3. With the SLOG device still selected, click Remove on the ZFS Info widget. Confirm and click Remove in the Remove device dialog to remove the device from the pool.

SCALE uses the storage disk resize command to change the size of a device. The SCALE UI does not have a UI function for this command yet. The storage disk resize command supports SAS, SATA, SAT (interposer) and NVMe drives. Power cycle SATA drives before a second resize.

1. Open a shell session using an SSH connection or from the local console.

2. Enter 6 from the TrueNAS console or enter cli in the Linux shell and press Enter to access the TrueNAS CLI. See the CLI Reference Guide for more information.

3. Enter storage disk query to return a table of all disks on the system and locate the row(s) for the disk you want to resize. Record the identifier, name, and current size of the disk.

   Unassigned disks are sometimes renamed when the system restarts. The identifier, in the format of serial_lunid, is a static value, which allows you to locate the correct disk to confirm changes after resizing.

4. Enter storage disk resize disks={"name":"sda", "size":"16"} where sda is the name of the disk and 16 is the new size for the disk (in gigabytes). If no size is specified, it reverts the provision back the full size of the device.

   The command returns the job progress completion percentage.

   storage disk resize disks={"name":"sda", "size":"16"}
   [0%] ...
   [100%] ...
   

5. Reboot the system.

6. Wait for the system to come online and then use the TrueNAS CLI to verify that the disk is resized to the correct capacity. Enter storage disk get_instance id="{serial_lunid}A1BCDEFG234567H_1234567a1234bc12" where A1BCDEFG234567H_1234567a1234bc12 is the disk identifier you recorded in step 3.

   storage disk get_instance id="{serial_lunid}A1BCDEFG234567H_1234567a1234bc12"
   +----------------+------------------------------------------------+
   |     identifier | {serial_lunid}A1BCDEFG234567H_1234567a1234bc12 |
   |           name | sds                                            |
   |      subsystem | scsi                                           |
   |         number | 16672                                          |
   |         serial | A1BCDEFG234567H                                |
   |          lunid | 1234567a1234bc12                               |
   |           size | 16013942784                                    |
   |    description |                                                |
   |   transfermode | Auto                                           |
   |     hddstandby | ALWAYS ON                                      |
   |   advpowermgmt | DISABLED                                       |
   |    togglesmart | true                                           |
   |   smartoptions |                                                |
   |     expiretime | <null>                                         |
   |       critical | <null>                                         |
   |     difference | <null>                                         |
   |  informational | <null>                                         |
   |          model | SAMSUNG_MZ7KM240HAGR-0E005                     |
   |   rotationrate | <null>                                         |
   |           type | SSD                                            |
   |       zfs_guid | 3102327624417314756                            |
   |            bus | ATA                                            |
   |        devname | sds                                            |
   |      enclosure | <dict>                                         |
   | supports_smart | <null>                                         |
   |           pool | <null>                                         |
   +----------------+------------------------------------------------+
   

   Confirm the target disk reports the updated size. Check if the reported name has changed. If so, record the new name.

7. Create a new pool or locate an existing pool on the Storage Dashboard and (re)assign the SLOG device to bring it online.

   To create a new pool with a SLOG device

   a. Go to Storage in the TrueNAS SCALE UI and click Create Pool to open the Pool Creation Wizard.

   b. Enter a name for the Pool and create at least one Data storage VDEV that fits your use case requirements.

   c. Click Log and select a Layout.

   d. Click Manual Disk Selection to open the Manual Selection dialog, click Add to add a VDEV, and search by name or serial number to locate the resized SLOG disk.

   e. Drag and drop the disk to the VDEV and click Save Selection.

   f. Add any other optional VDEVs as needed for your storage and performance requirements.

   e. Click Create Pool.

   See Create Pool for more information on using the Pool Creation Wizard.

   To (re)assign the SLOG device to an existing pool

   a. Go to Storage in the TrueNAS SCALE UI, locate the pool that you want to assign the SLOG device to and click Manage Devices on the Topology widget to open the Devices screen.

   b. Click Add VDEV to open the Add Vdevs to Pool screen.

   c. Click Log and select a Layout.

   d. Click Manual Disk Selection to open the Manual Selection dialog, click Add to add a VDEV, and search by name or serial number to locate the resized SLOG disk.

   e. Drag and drop the disk to the VDEV and click Save Selection.

   f. Go to Review and click Update Pool

   See Managing Pools for more information on using Add Vdevs to Pool.