Raid Card options: Write-through,write-back, write-around

Aim:Reducing latency in accessing data.

What is the difference between write-through, write-around, write-back?

Cache:Storing copy of data temporarily and local to CPU.

Write-through: is a storage method in which data is written in to the cache (RAM-Memory) and corrosponding main memory (disk-SAS/SATA etc.) location at same time. Select this option where data loss cannot be tolerated.


  • Minimize the risk of data loss.
  • safely.
  • Ensures that nothing will get lost if crash, power failure etc. low read latency.


  • Every write operation must be done twice and this redundancy takes a time.high write latency.

Write-back: is a storage method in which data is written in to the cache every time a change occurs but is written in to the disk(SAS/SATA etc.) only at specified intervals or under certain conditions.Select this option where data loss can be tolerated


  • Optimize system speed because it takes less time to write data into cache.


  • The risk of data loss in case of a crash or other adverse event.

Write-around: is a similar to write-through cache but write I/O is written directly to permanent storage (disks-SAS/SATA etc.) bypassing the cache.

How to setting cache setting on HP EVA storage?

From create virtual disk->Advance settings->Write cache policy: