From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brock Nanson Subject: Re: Md cache? Date: Thu, 03 Jun 2004 13:16:54 -0700 Sender: linux-raid-owner@vger.kernel.org Message-ID: <40BF8736.10101@nanson.org> References: <200406031922.i53JMS315198@watkins-home.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <200406031922.i53JMS315198@watkins-home.com> To: Guy Cc: 'Brian Pontius' , linux-raid@vger.kernel.org List-Id: linux-raid.ids My IBM ServeRAID 3HB's do. But as you say, many don't. A UPS with a communications cable and shutdown software is really the only solution. 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@vger.kernel.org > [mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Brian Pontius > Sent: Thursday, June 03, 2004 2:14 PM > To: Neil Brown > Cc: linux-raid@vger.kernel.org > 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 > Sent: Jun 2, 2004 10:10 PM > To: Brian Pontius > Cc: linux-raid@vger.kernel.org > Subject: Re: Md cache? > > On Wednesday June 2, linuxboy123@mindspring.com 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 > > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html