Write Policy - Write Cache Policy (Write-Back and Write Through)(RAID Settings).

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Write Cache Policy (Write-Back oraz Write Through)

Pamięć podręczna RAID to niewielka ilość pamięci, która przechowuje często używane dane w macierzy RAID, poprawiając wydajność i zmniejszając zużycie dysku. Istnieją jednak dwie różne metody zarządzania pamięcią podręczną RAID:

  • zapis zwrotny (Write-Back)
  • zapis przelotowy (Write-Through)

Polityka zapisu (Write Policy) ma ogromny wpływ na wydajność zapisu.

Write-Back RAID cache

  • RAID write-back cache is a mode in which the RAID controller writes data to the cache and immediately sends an acknowledgment to the host system without waiting for the data to be written to the disks. This means that write operations are faster and the host system can move on to other tasks. However, it also means that there is a risk of data loss or corruption if the cache fails or there is a power outage before the data is written to the disks. To mitigate this risk, a battery backup unit (BBU) or capacitor backup unit (CBU) should be installed in the RAID controller, which can preserve the contents of the cache in the event of a failure.
  • It is good practice to hook up the server to a UPS.
  • Method Required for RAID 5, 6.

Write-Through (Write-Thru)

  • RAID write-through cache is a mode in which the RAID controller writes data to the cache and to the disks at the same time and sends an acknowledgment to the host system only after the data is written to the disks. This means that write operations are slower and the host system has to wait longer. However, it also means that there is no risk of data loss or corruption in the event of a cache failure or power failure, since the data is already on the disks. You don't need a BBU or CBU on a RAID controller for a write-thru RAID cache.
  • Write Thru mode achieves the highest sequential write throughput for RAID 0 and RAID 10.

Related Pages:

  1. RAID Types 0, 1, 5, 6, 10, 50, 60 & RAID Calculator (What RAID level to choose for a server?)
  2. Supermicro Storage Platforms
  3. Supermicro AOC-S3108L-H8IR Broadcom 3108 SAS3 Raid Controller 1, 5, 6, 10, 50, 60
  4. Cable for Supermicro RAID, HBA, JBOD Controller - Compatibility Matrix
  5. New SAS-4 (24G) RAID controllers AOC-S4116L-H16IR and AOC-S4116L-H16IR-96DD available from Supermicro