Date: Mon, 01 May 2000 18:06:25 -0700 From: David Greenman <dg@root.com> To: Parag Patel <parag@cgt.com> Cc: Mike Smith <msmith@FreeBSD.ORG>, freebsd-stable@FreeBSD.ORG Subject: Re: How good is AMI MegaRAID support? Message-ID: <200005020106.SAA28942@implode.root.com> In-Reply-To: Your message of "Mon, 01 May 2000 18:01:26 PDT." <99363.957229286@pinhead.parag.codegen.com>
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>[Re: BSOD and system crashes, UPS and NVRAM] > >What if the RAID card's onboard software crashes? I don't know enough >about these cards to guess at what's more likely - FreeBSD crashing or >the onboard card software crashing. If they're about equally likely (or >unlikely) then NVRAM vs UPS still seems a wash to me. Depends on the RAID controller, but in general the data is recovered from the NVRAM after the controller reboots, so no data is lost. The recovery is broken, however, on the Infotrend controllers (at least the ones I evaluted), and it just gets stuck in an infinit loop crashing/restarting until you unplug the battery (there was a firmware bug in the recovery code - doh!). Needless to say, I wouldn't recommend Infortrend. :-) >Wouldn't any crashes that would toast a filesystem under FBSD care if >the underlying hardware was RAID or a single disk? Wouldn't it still be >toast either way? No. FreeBSD normally writes the filesystem metadata out in a way that the filesystem isn't toast when you have system failures. Defering writes removes that protection, however, so you better have NVRAM. >I can see how a NV write-buffer could speed up write performance, but >only if the disk writes are somewhat bursty. It doesn't seem to be very >different from disks with large onboard caches. (Which presumably might >still require a UPS to ride out crashes.) No, I think you don't understand the write performance issues of RAID-5. This is more than I want to get into discussing today, but I'll at least say that RAID-5 writes are *very* slow without a write-back cache. -DG David Greenman Co-founder/Principal Architect, The FreeBSD Project - http://www.freebsd.org Creator of high-performance Internet servers - http://www.terasolutions.com Pave the road of life with opportunities. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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