On Thu, Apr 08, 2010 at 12:14:55AM -0700, Erik Trimble wrote: > Daniel Carosone wrote: >> Go with the 2x7 raidz2. When you start to really run out of space, >> replace the drives with bigger ones. > > While that's great in theory, there's getting to be a consensus that 1TB > 7200RPM 3.5" Sata drives are really going to be the last usable capacity.
I dunno. The 'forces' and issues you describe are real, but 'usable' depends very heavily on the user's requirements. For example, a large amount of the extra space available on a larger drive may be very rarely accessed in normal use (scrubs and resilvers aside). In the OP's example of an ever-expanding home media collection, much of it will never or very rarely get re-watched. Another common use for the extra space is simply storing more historical snapshots, against the unlikely future need to access them. For such data, speed is really not a concern at all. For the subset of users for whom these forces are not overwhelming for real usage, that leaves scrubs and resilvers. There is room for improvement in zfs here, too - a more sequential streaming access pattern would help. To me, the biggest issue you left unmentioned is the problem of backup. There's little option for backing up these larger drives, other than more of the same drives. In turn, lots of the use such drives will be put to, is for backing up other data stores, and there again, the usage pattern fits the above profile well. Another usage pattern we may see more of, and that helps address some of the performance issues, is this. Say I currently have 2 pools of 1TB disks, one as a backup for the other. I want to expand the space. I replace all the disks with 2TB units, but I also change my data distribution as it grows: now, each pool is to be at most half-full of data, and the other half is used as a backup of the opposite pool. ZFS send is fast enough that the backup windows are short, and I now have effectively twice as many spindles in active service. > [..] it looks like hard drives are really at the end of their > advancement, as far as capacities per drive go. The challenges are undeniable, but that's way too big a call. Those are words you will regret in future; at least, I hope the future will be one in which those words are regrettable. :-) > >1TB drives currently have excessively long resilver time, inferior > reliability (for the most part), and increased power consumption. Yes, for the most part. However, a 2TB drive has dramatically less power consumption than 2x1TB drives (and less of other valuable resources, like bays and controller slots). > I'd generally recommend that folks NOT step beyond the 1TB capacity > at the 3.5" hard drive format. A general recommendation is fine, and this is one I agree with for many scenarios. At least, I'd recommend that folks look more closely at alternatives using 2.5" drives and sas expander bays than they might otherwise. > So, while it's nice that you can indeed seemlessly swap up drives sizes > (and your recommendation of using 2x7 helps that process), in reality, > it's not a good idea to upgrade from his existing 1TB drives. So what does he do instead, when he's running out of space and 1TB drives are hard to come by? The advice still stands, as far as I'm concerned: do something now, that will leave you room for different expansion choices later - and evaluate the best expansion choice later, when the parameters of the time are known. -- Dan.
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