On 09.06.2016, at 17:20, Duncan <1i5t5.dun...@cox.net> wrote: > Are those the 8 TB SMR "archive" drives?
No, they are Western Digital Red drives. Thanks for the detailed follow-up anyway. :) Half a year ago, when I evaluated hard drives, in the 8 TB category there were only the Hitachi 8 TB Helium drives for 800 bucks, and the Seagate SMR for 250 bucks. I bought myself one of the Seagate SMR ones for testing, and figured out it wouldn't work for my use case (I now use it in a write-very-seldom context). For my two NASes I went with 6 TB WD Red drives all around. Nowadays there are more choices of 8 TB drives, such as the WD Reds I'm switching my backup NAS to. > I haven't been following the issue very closely, but be aware that there > were serious issues with those drives a few kernels back, and that while > those issues are now fixed, the drives themselves operate rather > differently than normal drives, and simply don't work well in normal > usage. > > The short version is that they really are designed for archiving and work > well when used for that purpose -- a mostly write once and leave it there > for archiving and retrieval but rarely if ever rewrite it, type usage. > However, they work rather poorly in normal usage where data is rewritten, > because they have to rewrite entire zones of data, and that takes much > longer than simply rewriting individual sectors on normal drives does. > > With the kernel patches to fix the initial problems they do work well > enough, tho performance may not be what you expect, but the key to > keeping them working well is being aware that they continue to do > rewrites in the background for long after they are done with the initial > write, and shutting them down while they are doing them can be an issue. > > Due to btrfs' data checksumming feature, small variances to data that > wouldn't normally be detected on non-checksumming filesystems were > detected far sooner on btrfs, making it far more sensitive to these small > errors. However, if you use the drives for their intended nearly write- > only purpose, and/or very seldom power down the drives at all or do so > only long after (give it half an hour, say) any writes have completed, as > long as you're running a current kernel with the initial issues patched, > you should be fine. Just don't treat them like normal drives. > > If OTOH you need more normal drive usage including lots of data rewrites, > especially if you frequently poweroff the devices, strongly consider > avoiding those 8 TB SMR drives, at least until the technology has a few > more years to mature. > > There's more information on other threads on the list and on other lists, > if you need it and nobody posts more direct information (such as the > specific patches in question and what specific kernel versions they hit) > here. I could find it but I'd have to do a search in my own list > archives, and now that you are aware of the problem, you can of course do > the search as well, if you need to. =:^) > > -- > Duncan - List replies preferred. No HTML msgs. > "Every nonfree program has a lord, a master -- > and if you use the program, he is your master." Richard Stallman > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
