On 2016-08-09 06:02, Gim Leong Chin wrote:
>> Drives connected to RAID controllers with battery backed cache should
>> have their caches "disabled" (they are really set to write through mode
>> instead). By the way, I found out in lab testing that 7200 RPM SATA
>> drives suffer a big performance loss when doing sequential writes in
>> cache write through mode.<
> If you disable the disk internal cache, as a consequence you also
> disable the disk internal write optimizations. It has to be much slower
> at writing. It seems to me obvious.
> --
> Cheers / Saludos,
> Carlos E. R.
>> Drives connected to RAID controllers with battery backed cache should
>> have their caches "disabled" (they are really set to write through mode
>> instead). By the way, I found out in lab testing that 7200 RPM SATA
>> drives suffer a big performance loss when doing sequential writes in
>> cache write through mode.<
> If you disable the disk internal cache, as a consequence you also
> disable the disk internal write optimizations. It has to be much slower
> at writing. It seems to me obvious.
> --
> Cheers / Saludos,
> Carlos E. R.
> (from 13.1 x86_64 "Bottle" at Telcontar)
The drop in sequential write data rate for 3.5" 7200 RPM SATA drives was around 50%, I cannot remember the exact numbers, that is not obvious to me.
As a reminder, the drive cache is really set to write through mode, it is not possible to disable the cache, as an application engineer from HGST told me, so the drive internal write optimizations are still there, just that the IO command is reported to be completed only when the data has been writen to the drive platter.
10k and 15k RPM SAS drives connected to LSI Internal RAID controllers have their drive cache "disabled" automatically, I wonder how much is the data rate drop compared to drive cache "enabled", considering that LSI IR controllers do not have cache.
GL
As a reminder, the drive cache is really set to write through mode, it is not possible to disable the cache, as an application engineer from HGST told me, so the drive internal write optimizations are still there, just that the IO command is reported to be completed only when the data has been writen to the drive platter.
10k and 15k RPM SAS drives connected to LSI Internal RAID controllers have their drive cache "disabled" automatically, I wonder how much is the data rate drop compared to drive cache "enabled", considering that LSI IR controllers do not have cache.
GL
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