Question: 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?
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:
- http://www.tansi.org/hybrid/ (“Hybrid HDD + SSD RAID1”)
- http://linuxwiki.de/SSD (overview, hints; in German)
- http://marc.info/?l=linux-raid&m=126496930530289&w=2 (“SSD & mechanical disc in RAID 1”)