Tuesday, March 13, 2018

RAID controller evolution in Exadata

Some things do not lie on the surface, an interesting moment was found out in the Exadatas X7-2 and X6-2: a RAID controller lost a battery. In previous generations of Exadata the RAID controller had a battery.

On the one hand to live without a battery
is even better: you do not need to change them. But on the other hand, is there no more way to have a Write-Back cache on RAID controller?






1. Cells with High Capacity disks:

Х7-2 Disk controller HBA with 2 GB cache
Х6-2 Disk controller HBA with 1 GB cache
Х5-2 Disk controller HBA with 1 GB supercap-backed write cache
Х4-2 Disk controller HBA with 512 MB battery-backed write cache, and swappable BBU
Х3-2 Disk controller HBA with 512 MB battery-backed write cache
Х2-2 Disk controller HBA with 512 MB battery-backed write cache

2. Database servers lost the battery too:

Х7-2 Disk controller HBA with 2 GB cache (no batteries)
Х6-2 Disk controller HBA with 1 GB cache (no more batteries)
Х5-2 Disk controller HBA with 1 GB supercap-backed write cache
Х4-2 Disk controller HBA with 512 MB battery-backed write cache, and swappable battery backup unit (BBU)
Х3-2 Disk controller HBA with 512 MB battery-backed write cache, and swappable battery backup unit (BBU)
Х2-2 Disk controller HBA with 512 MB battery-backed write cache

Is there no more way to have a Write-Back cache on RAID controller?
No! in the X7 and X6 oracle use the capacitor instead of battery.
So write-back will take place and write IO promises to be excellent.

3.
Is there RAID controller in the Extreme Flash cells ?
NO: Extreme flash cards directly attached to PCI, so there is no any RAID controller in EF-cells.


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