Brock
Guy wrote:
With hardware RAID the write cache has battery backup. So, the RAID system will not lose data when the power fails. It will finish the writes when the power returns.
I don't think the hardware RAID cards have a battery. The external self contained RAID systems that I have worked with do have batteries.
Anyone know? Do any RAID cards have batteries?
Guy
-----Original Message----- From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Brian Pontius Sent: Thursday, June 03, 2004 2:14 PM To: Neil Brown Cc: linux-raid@xxxxxxxxxxxxxxx Subject: Re: Md cache?
I apologze for being unclear.
As I did comparisons between software and hardware raid, one of the advantage s that I noticed with hardware raid was cache (both read and write). With hard ware it is usually larger giving some increase in performance. I was looking for a way to allocate more system memory specifically to be the md cache area to give that extra feature of that hardware raid. This would especially be ben efitial for a NAS that has a dedicated purpose to fast reliable storage.
Thanks for your time. Brian Pontius
-----Original Message----- From: Neil Brown <neilb@xxxxxxxxxxxxxxx> Sent: Jun 2, 2004 10:10 PM To: Brian Pontius <linuxboy123@xxxxxxxxxxxxxx> Cc: linux-raid@xxxxxxxxxxxxxxx Subject: Re: Md cache?
On Wednesday June 2, linuxboy123@xxxxxxxxxxxxxx wrote:
to all,
Is anyone aware of a way to cause the md devices to use some system memory
as a write cache? (maybe through mdadm?). I have looked everywhere and cannot seem to find anything about such a feature.
If not, anyone know if this is a possibility for the future, Neil?
What is it exactly that you want.
All device IO is cached in memory before being written to the device. The only real value of a cache with a RAID array is if it we a non-volatile cache. Is that what you were thinking of.
NeilBrown
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