On Thu, Jun 16, 2011 at 07:06:48PM +0200, Roy Sigurd Karlsbakk wrote: > > I have decided to bite the bullet and change to 2TB disks now rather > > than go through all the effort using 1TB disks and then maybe changing > > in 6-12 months time or whatever. The price difference between 1TB and > > 2TB disks is marginal and I can always re-sell my 6x 1TB disks. > > > > I think I have also narrowed down the raid config to these 4; > > > > 2x 7 disk raid-z2 with 1 hot spare - 20TB usable > > 3x 5 disk raid-z2 with 0 hot spare - 18TB usable > > 2x 6 disk raid-z2 with 2 hot spares - 16TB usable > > > > with option 1 probably being preferred at the moment. > > I would choose option 1. I have similar configurations in > production. A hot spare can be very good when a drive dies while > you're not watching.
I would probably also go for option 1, with some additional considerations: 1 - are the 2 vdevs in the same pool, or two separate pools? If the majority of your bulk data can be balanced manually or by application software across 2 filesystems/pools, this offers you the opportunity to replicate smaller more critical data between pools (and controllers). This offers better protection against whole-pool problems (bugs, fat fingers). With careful arrangement, you could even have one pool spun down most of the time. You mentioned something early on that implied this kind of thinking, but it seems to have gone by the wayside since. If you can, I would recommend 2 pools if you go for 2 vdevs. Conversely, in one pool, you might as well go for 15xZ3 since even this will likely cover performance needs (and see #4). 2 - disk purchase schedule With 2 vdevs, regardless of 1 or 2 pools, you could defer purchase of half the 2Tb drives. With 2 pools, you can use the 6x1Tb and change that later to 7x with the next purchase, with some juggling of data. You might be best to buy 1 more 1Tb to get the shape right at the start for in-place upgrades, and in a single pool this is essentially mandatory. By the time you need more space to buy the second tranche of drives, 3+Tb drives may be the better option. 3 - spare temperature for levels raidz2 and better, you might be happier with a warm spare and manual replacement, compared to overly-aggressive automated replacement if there is a cascade of errors. See recent threads. You may also consider a cold spare, leaving a drive bay free for disks-as-backup-tapes swapping. If you replace the 1Tb's now, repurpose them for this rather than reselling. Whatever happens, if you have a mix of drive sizes, your spare should be of the larger size. Sorry for stating the obvious! :-) 4 - the 16th port Can you find somewhere inside the case for an SSD as L2ARC on your last port? Could be very worthwhile for some of your other data and metadata (less so the movies). -- Dan.
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