Configuring the Read Cache and Write Log
SoftNAS® provides the ability to add Read Cache and Write Log devices to a storage pool. Read Cache provides an additional layer of cache, in addition to RAM memory cache. The Write Log provides a cache for incoming writes to be written temporarily to high-speed storage, then later staged to lower-speed spindle-based storage. SSD is recommended for both Read Cache and Write Log.
A Write Log is also referred to as a ZIL.
Important
The Write Log becomes a critical element of the storage pool, so it is highly recommended to always use a RAID 1 mirror for Write Log (that way, if a write log device fails, the storage pool won't be at risk of invalidation because the write log is now an integral part of the pool). Please click on the KB link Adding ZFS Intent Log/SLOG and L2ARC for SoftNAS Pools and you will know if you need to add Read Cache or Write Log.
Buurst recommends the creation of a write log for all instances using SnapReplicate and SNAP HA for high availability.
- Navigate to Storage > Storage Pools under the Storage Administration pane. The Storage Pools panel will be displayed with the list of all the existing storage pools that are already allocated.
Create required storage pools as previously defined here.
Ephemeral disks can be used in a pool created for caching purposes if the platform used supports this option (AWS and Azure). However, the first time they are used in a pool, the 'force' option must be used to overwrite the default file-system. Remember that ephemeral devices are non-persistent and wiped on reboot.Verify that disk drives are available that have not been assigned to other storage pools.
These should be high-speed drives: SAS or SSD.
Configure Read Cache
- On the Storage Pools - Pool Details panel, click the Details tab in the lower left corner.
- Verify that no cache is listed under Pool Devices.
- Select the Storage Pool in which you want to add Read Cache.
- Click the Read Cache button in the Pools Grid toolbar towards the top of the page. The Add Read Cache to Storage Pool dialog box will be displayed.
- Select the disk to you wish to use for Read Cache.
- Click the Add Cache button.
Configure Write Log
- On the Storage Pools - Pool Details panel, click the Details tab in the lower left corner.
- Verify that no log is listed under Pool Devices.
- Select the Storage Pool in which you want to add Write Logs.
- Click the Write Log button in the Pools Grid toolbar towards the top of the page. The Add Write Log Devices to Storage Pool dialog box will be displayed.
- Select the disk to you wish to use for Write Logs.
- Click the Add Log button.
- Log and Cache devices can be viewed in the Pool Details pane.
