From owner-freebsd-stable Sun Jan 21 21:18: 2 2001 Delivered-To: freebsd-stable@freebsd.org Received: from mass.dis.org (ashto-0006.sjc.ca.bbnow.net [24.219.121.199]) by hub.freebsd.org (Postfix) with ESMTP id 748A937B400 for ; Sun, 21 Jan 2001 21:17:44 -0800 (PST) Received: from mass.dis.org (localhost [127.0.0.1]) by mass.dis.org (8.11.1/8.11.1) with ESMTP id f0M5VqD01716; Sun, 21 Jan 2001 21:32:08 -0800 (PST) (envelope-from msmith@mass.dis.org) Message-Id: <200101220532.f0M5VqD01716@mass.dis.org> X-Mailer: exmh version 2.1.1 10/15/1999 To: "Jim C. Nasby" Cc: Mike Tancsa , Sys Admin , freebsd-stable@freebsd.org Subject: Re: RAID configuration for a mail server (1 or 5) In-reply-to: Your message of "Sat, 20 Jan 2001 01:26:00 CST." <3A693D88.9D1F4E3D@nasby.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Sun, 21 Jan 2001 21:31:52 -0800 From: Mike Smith Sender: owner-freebsd-stable@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > Mike Tancsa wrote: > > For speed, reliability and cost, have a look at the 4port 3ware card > > (www.3ware.com) in RAID 10 config. Two RAID0 sets mirrored together. Get > > FWIW, a RAID0 of RAID1 sets is more desireable. When one of the drives > fails, you only have to rebuild one drive, using it's mirrored > counterpart. In the other case, you have to rebuild an entire RAID0 set > from another set, tying up every drive in the system. This depends on how smart the RAID controller is; AFAIR the 3ware controller is actually doing striped "TwinStor" groups, but I'm on the road and would have to check when I get home. > Also, depending on > how the mirroring is done, simultaneous failure of a drive on each > mirror could render you without any data. While it would be really bad > luck to lose two drives at once, the odds losing one on each mirror are > far greater than losing both drives in a two-drive mirror that happens > to be part of a stripe set. I'd have a hard time accepting that 10+ years into the evolution of RAID technology, anything other than a dime-store controller would do this. 8) > BTW, if memory serves, the downside that RAID 5 has over RAID 0 is that > in order to update a segment of the set, you must first read the entire > segment in, then recalculate it with the changed data, then write the > changes back out. This will very often result in 2x the number of r/w > operations as the number of drives. Um, I'd recommend a quick RAID-101 course. 8) You can read the original data block, the checksum block, and from the delta between the original block, the new data and using the checksum data you can regenerate the checksum. This typically involves two reads and two writes for a given write, although normally the reads are performed on a fairly large block to improve sequential performance (some will read a whole stripe, others like eg. Mylex use 8k (default) 'cache lines' as the basic unit for this operation). You only actually have to read the data that backs the data being written though. -- ... every activity meets with opposition, everyone who acts has his rivals and unfortunately opponents also. But not because people want to be opponents, rather because the tasks and relationships force people to take different points of view. [Dr. Fritz Todt] V I C T O R Y N O T V E N G E A N C E To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message