Date: Sun, 30 Jan 2000 21:17:10 -0800 (PST) From: Tom <tom@sdf.com> To: Greg Lehey <grog@lemis.com> Cc: Marc Tardif <admin@wtbwts.com>, freebsd-scsi@FreeBSD.ORG Subject: Re: hardware vs software stripping Message-ID: <Pine.BSF.4.05.10001302107360.5637-100000@misery.sdf.com> In-Reply-To: <20000131120326.D62824@freebie.lemis.com>
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On Mon, 31 Jan 2000, Greg Lehey wrote: > 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. Well, since I still can order the DPT 3334, I think its demise is greatly exagerated... as far as performance goes, it is not a new design and can't keep the new disks busy. Second, a DPT can't do RAID 5 + 0. It does the RAID 5 in hardware. The RAID 5 you'll have to do in software. > > 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. Depends on the database. Many databases allow the additional of storage on any device, so there shouldn't be a problem. An Infortrend (see below) can do a transparent copy-and-replace array expansion. This however just leaves you with a bigger virtual disk. FreeBSD has no way to grow a filesystem transparently. You can disklabel the addtional space and make a new filesystem though. > >>> 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. I don't think you can access the on-board management of any of the HBA RAID cards under FreeBSD. A SCSI-SCSI RAID controller (like a Infortrend or Mylex) is pretty nice. You can manage them. The Infortrend support RAID 5 + 0 in hardware. As far as vinum goes, I don't see how I can use to make a mirrored system disk (root and swap). I don't know if that will even be possible on x86 architecture. > Greg > -- > Finger grog@lemis.com for PGP public key > See complete headers for address and phone numbers Tom To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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