How to change between the Write-through Cache and Write-Back Cache on Storage?

Issue

• How to change/switch between the Write-through Cache and Write-Back Cache on the storage end?
• To perform a disk benchmark through a virtual machine it is recommended to disable virtual disk write-cache.
• What are the different methods of changing the on-disk write cache settings?
• Which versions of RHEL support hdparm use?
• Which versions of RHEL support sdparm use?
• What are the alternatives to sdparm or hdparm use for changing write cache setting on a block device?
• Why does sdparm work but hdparm fail to report or change write cache setting on a block device?
• How to ensure written data integrity to a block device?
• How do I ensure that data is securely and reliably written to disk?
• What is meant by enabling 'Fast Writes' to improve io write performance?
• How to enable/disable caching for block device.
• When editing a file on block device the write operation will not take place immediately because of caching is enabled.

• When discovering the LUN, the linux kernel enables "write-through" for the AMS1000 and "write-back" for the AMS2300.

  • The "write-through" gives poor performances in this situation. How can I force linux to enable the "write back" feature ?

    Feb 14 11:29:56 kernel:   Vendor: HITACHI   Model: DF600F            Rev: 0000
    Feb 14 11:29:56 kernel:   Type:   Direct-Access                      ANSI SCSI revision: 03
    Feb 14 11:29:56 kernel: SCSI device sda: 122159104 512-byte hdwr sectors (62545 MB)
    Feb 14 11:29:56 kernel: sda: Write Protect is off
    Feb 14 11:29:56 kernel: SCSI device sda: drive cache: write through ( ====> AMS 1000 <=======)
    Feb 14 11:29:56 kernel:  sda: sda1
    Feb 14 11:29:56 kernel: sd 0:0:0:0: Attached scsi disk sda
    
    Feb 14 11:29:56 kernel:   Vendor: HITACHI   Model: DF600F            Rev: 0000
    Feb 14 11:29:56 kernel:   Type:   Direct-Access                      ANSI SCSI revision: 04
    Feb 14 11:29:56 kernel: SCSI device sdb: 2097152 512-byte hdwr sectors (1074 MB)
    Feb 14 11:29:56 kernel: sdb: Write Protect is off
    Feb 14 11:29:56 kernel: SCSI device sdb: drive cache: write back (=======> AMS 2300 <============)
    Feb 14 11:29:56 kernel:  sdb: sdb1
    Feb 14 11:29:56 kernel: sd 0:0:1:1: Attached scsi disk sdb