Linux – combining SSD and hard disk in software RAID1

hard drivelinuxraid-1software-raidssd

Does it make sense to build a Linux software RAID-1 (mirroring) using an SSD and a normal hard disk? I want to combine the advantages of SSD (fast transfer rates, fast access times) with the advantages of hard disks (cheap, different fault model) and get a very fast yet reliable RAID…

  • does this actually make sense?
  • is the SSD performance actually available in such a mixed setup? I.e. does Linux mainly use SSD for reading, or will it use the slow disk equally much?

Best Answer

Looks like this setup is quite ok. The basic rule is to use mdadm with --write-mostly parameter so that writes go to HDD. Reading will still be done from fast SSD. Also, the --write-behind parameter is said to improve write performance.

Support for TRIM command in such a setup appears to be a problem, though.

Further keywords for searching:

  • linux ssd raid hybrid
  • mdadm "--write-mostly" ssd

Further links:

Related Question