Date: Sun, 2 Apr 1995 09:55:58 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: peter@bonkers.taronga.com (Peter da Silva) Cc: terry@cs.weber.edu, PVinci@ix.netcom.com, hackers@FreeBSD.org Subject: Re: large filesystems/multiple disks [RAID] Message-ID: <199504021655.JAA01937@gndrsh.aac.dev.com> In-Reply-To: <199504021351.IAA02419@bonkers.taronga.com> from "Peter da Silva" at Apr 2, 95 08:51:25 am
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> > > > > It's fragile because you could for instance have four file systems > > > > with blocks in the same 16M area of a disk. > > > > Um, why would you do that? Doesn't that sort of counter the whole reason > > > for running file systems over multiple disks? > > > I would think so, the way Auspex handles this is that the blocking factor > > can be tuned when the logical volume is created. [...] > > You miss the point. Why would you have multiple file systems on the same > set of disks? To keep there sizes from becoming unmanagable. We where stripping 3Gbyte drives and we didn't want any logical volume to be larger than our dump tape capacity (5GBytes). We ended up with 4 wide stripes (12GB total) split into 3 logical drives of 4 GB each. > > [goes on to describe the performance benefits of striping] > > Yeh, then it becomes useful... but if you're going to that effort you'd go > full RAID with parity, so a disk failure just means you slip another disk > in and let it repopulate it. Yeh, it's more complex... but so is striping. Auspex's don't use raid, and have been doing disk stripping for a long time. With MTBF's >800K hours on modern disk drives failure has become much less of an issue. RAID does have the negative effect of of having to write 20% more data, thus cutting effective bandwidth by 20%. It is actually worse than this in that all writes must write to at least 2 drives no matter how small they are. The removes some of the benifits of stripping. -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Custom computers for FreeBSD
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