> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Roy Sigurd Karlsbakk > > With 2TB drives priced at €150 or lower, I somehow think paying for > drive lifetime is far more expensive than getting a few more drives and > add redundancy
If you have a 48-disk enclosure, and you've configured 6x 8disk raid-6 or raidz2 volumes, how do you add more disks to increase redundancy? Point is: Adding disks often means adding slots, and since adding slots ain't free, it would generally translate not so much as adding slots, but decreasing the number of usable drive capacities... And keeping an inventory of offline spares for the sake of immediate replacement upon failure. Also, you'll only find the cheapest generic disks available at the stated price. If you have one of those disks fail 6 months from now, you will not be able to purchase that model drive again. (God forbid you should have to replace one 3 yrs from now, when the current implementation of SAS or SATA isn't even for sale anymore, and you can't even get a suitable "equivalent" replacement.) I hate it whenever people over-simplify and say "disk is cheap." Also, if you've got all those disks in an array, and they're MTBF is ... let's say 25,000 hours ... then 3 yrs later when they begin to fail, they have a tendency to all fail around the same time, which increases the probability of exceeding your designed level of redundancy. I recently bought 2x 1Tb disks for my sun server, for $650 each. This was enough to make me do the analysis, "why am I buying sun branded overpriced disks?" Here is the abridged version: We recently had an Apple XRAID system lose a disk. It's 3 yrs old. It uses 500G ATA-133 disks, which are not available from anywhere at any price... Except Apple was willing to sell us one for $1018. Naturally, we declined to make that purchase. We did find some disks available from various sources, which should be equivalent, but not Apple branded or certified; functional equivalents but not identical. Prices around $200 to $300. I asked around, apple admins who had used generic disks in their Xraid systems. About 50% said they used generic disks with no problem. The other 50% were mixed between "we used generic disks, seemed to work, but had strange problems like horrible performance or disk suddenly going offline and coming back online again spontaneously" and "we tried to use generic disks, but the system refused to even acknowledge the disk present in the system." Also, take a look in the present mailing list, many people complaining of drives with firmwares that incorrectly acknowledge cache flushes before they're actually flushed. Even then, we're talking about high end Intel SSD's. And the consequence of incorrect firmware is data loss. Maybe even pool loss. The reason why we pay for overpriced disks is to get the manufacturer's seal of approval, the Apple or Sun or Dell branded firmware. The availability of mfgr warranties, the long-term supportability. It costs about 4x-5x more per disk to buy up front, but since you have to buy 2x as many generic disks (for the sake of spare inventory availability) you're only paying 2x overall, and you can rest much more assured in the stability. Even at the higher hardware price, the value of the data is presumed to be much greater than the cost of the hardware. So then it's easy to justify higher cost hardware, with the belief it'll be somehow lower data risk. Sometimes people will opt for cheaper. Sometimes people will opt for lower risk. I just hate it when people oversimplify and say "disk is cheap." That is so over simplified, it doesn't benefit anyone. <end rant> <begin breathe> ... _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
