Tag: ssd

SSD Cache Basic

SSD Cache Basic


SSD cache helps accessing same set of files frequently. But if the system just holding media files, most likely they won't be visited again, then cache doesn't help.

RAM is required for SSD cache, but adding RAM is more directly impact the perform, because there is no duplication between harddisk and SSD.


The required amount of RAM is calculated before cache created.

One SSD disk only can be configured for one volume in read-only mode.

Two or more SSD disks can be configured as one raid, for one volume in read-write mode.

Currently, one SSD disk or raid can not be partitioned for different volume.

FreeNAS/TrueNAS (Untested)

Others suggest 64GB or more of RAM before adding a cache, otherwise, will slow the system down if add a cache with 16GB RAM.

Fusion disk could be another choise because the SSD can be used as storage as well, no waste of space.

TODO: Synology SSD Cache Issues

Synology SSD Cache Issues

Synology SSD Cache have two issues as below

  • Unable to use one disk/array to support mulitiple volume.

    • No answer from Internet and some people mentioned that it is a new request.
    • Possible solution is to create partition/volume on SSD Storage Pool, then use volume as cache device.
    • Synology uses LVM cache, haven't checked whether native linux can do or not.
  • Utilization of cache is very low, about 5GB on fequently used volume, such as volume1.

    • Improved in DSM 7 which supports Pin all Btrfs metadata option. But haven't validated the utilization.