On Fri, Jul 25, 2008 at 1:02 PM, Matt Wreede <[EMAIL PROTECTED]> wrote: > Howdy. > > My plan: > > I'm planning an ESX-iSCSI target/NFS serving box. > > I'm planning on using an Areca RAID card, as I've heard mixed things about > hot-swapping with Solaris/ZFS, and I'd like the stability of a hardware RAID. > > My question is this: I'll be using 8 750GB SATA drives, and I''m trying to > figure out the best method to maintain: > 1) Performance > 2) Hot-swap-ability > 3) Disk loss. > > My current plan is to build two RAID-5 arrays, 4 drives each, and mirror them > in ZFS and add them to the pool. This will give me 750GB*3, size wise, total. > > Now, here is the important question: Does mirroring provide a performance > boost, or is it simply a way to provide redundancy? That is, if I go ahead > and force-add the RAID-5 arrays, without mirroring them, I'll have 6 usable > drives; double the storage, but ZFS won't see any redundancy. But if a drive > fails, ZFS won't know or care, I'll simply go into the Areca control panel > and eject the drive; voila! > > But, is there a performance boost with mirroring the drives? That is what I'm > unsure of. > > Thanks for any information! >
I know that if your mind is made up, in terms of using the Areca, then this post is probably not going to change it, but I'd still like to give you some food for thought. If it were me, I would not add the Areca (which, BTW, is a fine piece of hardware) because: a) cost; or, put another way, those $s can be applied elsewhere with more payback in terms of performance etc. (more below) b) You're mixing "software" (in the case of the Areca it's more correctly called firmware) from 2 vendors - to provide a storage solution where both vendors have fundamentally different approaches to solving the same (storage) problem. c) Now you've got to maintain and "patch" both vendors "software" stacks. e) Fundamentally, ZFS is designed to talk *directly* to disk drives. f) the current issues/deficiencies you point out with todays ZFS implementation *will* vanish over time as ZFS is still under very active development. So you're "solving" a problem that will solve itself in a relatively short timeframe. g) the disk drives are tied to the hardware RAID controller - you can't migrate the disks to another box without buying another (compatible) RAID controller. If your RAID controller dies you're SOL. h) your performance will be limited to the performance (today) of the RAID hardware - rather than to the massive performance advantage you'd gain by upgrading the system to a new motherboard/processor in a years time (Nahelem for example). I'll assume that you're going to spend $500 on the hardware RAID controller (because I don't know which model/config you're thinking of). So, the question that I propose here (and attempt to answer) is: "can those $500s be spent on a ZFS only solution to provide better value"? Proposal 1): Buy an LSI based SAS controller board and a couple of 15k RPM SAS drives (you get to pick the size) and configure them as ZFS log (slog) and cache devices. Benefit: improved NFS performance. Overall improved system performance. Proposal 2): Buy as much RAM as possible. ZFS loves RAM. How about 16Gb or more. Yep - that'll work! :) Proposal 3) Put the $500 in the stock market and wait for Sun to release their "enterprise" RAM/Flash (or whatever it'll be) SSD. This will provide a *huge* performance gain, especially for NFS. And this will be a simple "push in" type upgrade.[0] Proposal 4) SAS solution similar to proposal 1 - but use the 15k SAS disks to provide a ZFS mirrored pool with lots of IOPS. Remember there is *no* RAID storage configuration that is "right" for every work load and my advice is always to configure multiple RAID configs to support different workloads[1]. Also, your work load scenarios may change over time, in ways that you did'nt foresee. Proposal 5) Since you'll be providing iSCSI, please do yourself a big favor and install an enterprise level (multiple ports??) ethernet card (Sun has one). Otherwise the tens of thousands of interrupts/Sec caused by iSCSI ops will *kill* your overall system performance. The reason why an enterprise card helps is because it'll coalesce those interrupts and leave the system CPU cores free to do useful work. [0] and you'll probably need to be a really good investor to be able to afford it! :) [1] on a 10-disk system here, there's a 5-disk raidz1 pool, a 2-disk mirror and a 3-disk mirror. If I were to do it again, I'd push for a 6-disk raidz2 pool in place of the raidz1 pool. Regards, -- Al Hopper Logical Approach Inc,Plano,TX [EMAIL PROTECTED] Voice: 972.379.2133 Timezone: US CDT OpenSolaris Governing Board (OGB) Member - Apr 2005 to Mar 2007 http://www.opensolaris.org/os/community/ogb/ogb_2005-2007/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
