3.4 Maintaining Flash Disks on Oracle Exadata Storage Servers

Data is mirrored across Exadata Cells, and write operations are sent to at least two storage cells. If a flash card in one Oracle Exadata Storage Server has problems, then the read and write operations are serviced by the mirrored data in another Oracle Exadata Storage Server. No interruption of service occurs for the application.

If a flash card fails while in write-back mode, then Oracle Exadata System Software determines the data in the flash cache by reading the data from the mirrored copy. The data is then written to the cell that had the failed flash card. The location of the data lost in the failed flash cache is saved by Oracle Exadata System Software at the time of the flash failure. Resilvering then starts by replacing the lost data with the mirrored copy. During resilvering, the grid disk status is ACTIVE -- RESILVERING WORKING. If the cache is in write-through mode, then the data in the failed device is already present on the data grid disk, so there is no need for resilvering.

• Replacing a Flash Disk Due to Flash Disk Failure
  Each Oracle Exadata Storage Server is equipped with flash devices.
• About Flash Disk Degraded Performance Statuses
  If a flash disk has degraded performance, you might need to replace the disk.
• Replacing a Flash Disk Due to Flash Disk Problems
  
• Performing a Hot Pluggable Replacement of a Flash Disk
  Starting with Oracle Exadata Database Machine X7, flash disks are hot-pluggable on both Extreme Flash (EF) and High Capacity (HC) storage servers.
• Enabling Write Back Flash Cache
  Write operations serviced by flash instead of by disk are referred to as write-back flash cache.
• Disabling Write Back Flash Cache
  You can disable the Write-Back Flash Cache by enabling Write-Through Flash Cache.
• Monitoring Exadata Smart Flash Cache Usage Statistics