From owner-freebsd-scsi Sun Jan 30 17:33:45 2000 Delivered-To: freebsd-scsi@freebsd.org Received: from freebie.lemis.com (freebie.lemis.com [192.109.197.137]) by hub.freebsd.org (Postfix) with ESMTP id 2CE4A15274 for ; Sun, 30 Jan 2000 17:33:41 -0800 (PST) (envelope-from grog@freebie.lemis.com) Received: (from grog@localhost) by freebie.lemis.com (8.9.3/8.9.0) id MAA63457; Mon, 31 Jan 2000 12:03:26 +1030 (CST) Date: Mon, 31 Jan 2000 12:03:26 +1030 From: Greg Lehey To: Marc Tardif Cc: freebsd-scsi@FreeBSD.ORG Subject: Re: hardware vs software stripping Message-ID: <20000131120326.D62824@freebie.lemis.com> References: <20000131104827.A62824@freebie.lemis.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0pre2i In-Reply-To: WWW-Home-Page: http://www.lemis.com/~grog X-PGP-Fingerprint: 6B 7B C3 8C 61 CD 54 AF 13 24 52 F8 6D A4 95 EF Organization: LEMIS, PO Box 460, Echunga SA 5153, Australia Phone: +61-8-8388-8286 Fax: +61-8-8388-8725 Mobile: +61-41-739-7062 Sender: owner-freebsd-scsi@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org On Sunday, 30 January 2000 at 20:04:18 +0000, Marc Tardif wrote: > On Mon, 31 Jan 2000, Greg Lehey wrote: > >> On Sunday, 30 January 2000 at 14:24:54 +0000, Marc Tardif wrote: >>> ... >>> using postgresql. The alternatives are either raid-1 which seems too >>> wasteful on disks or raid-5 which provides fault tolerance. This last >>> option could substituted for a tape backup and the possibility of a few >>> minutes down time in case of disk failure. >> >> I'm not sure I understand this sentence. Are you planning to forget >> RAID-5 after all and use a tape backup? For reasonably large disks, >> your downtime will be measured in hours, not minutes. For a RAID-5 >> array, you shouldn't get any down time. > > You understood correctly, but I guess you're right. From reading the > dpt.com website, hardware failures are caused by hard-drives 50% of the > time. Also, from one of Simon Shapiro's posting to this mailing list, I > could build a raid 0+5 array which would seem to be an optimal solution > for a database performing random reads and writes. Therefore, I should > probably forget simply using ccd or vinum for a production system. I don't know how you conclude that. First, the DPT probably won't buy you anything in terms of performance, and secondly it's out of production. > There is another problem though, which is that I can't really have a > general idea of the amount of space I'll require. Therefore, from my > understanding, if I need to expand an array containing an sql db, I'll > need to rebuild the whole thing after recreating a new filesystem on the > new array. I'd be very relieved if there was an easier way... I can't make qualified statements about SQL. >>> For software, I think freebsd's ccd could provide all the services >>> required for very fast i/o on a straight array of disks and at a >>> fraction of the cost of the raid alternative. Unfortunately, I have >>> never witnessed the virtues of raid myself and I am not in a >>> position to make an educated decision. I would therefore appreciate >>> if someone from this mailing list could share their experience to >>> help with my dilemna. >> >> Why do you want to use ccd and not vinum? In any case, you may find >> that either are faster than the DPT controller (if you can find one; >> they're no longer making them). > > The more I read about raid, the more I think it could be worthwhile. > Although it can be expensive, I want to make sure I get what the server > needs. As for getting a DPT controller, what's this about "the DPT > controller" not being made anymore? That's my understanding. Even if you can get one, the performance is disappointing. In addition, I don't think you can't access the on-board management software from FreeBSD. Greg -- Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message