On Thu, Jan 2, 2020 at 1:41 PM Dale <[email protected]> wrote: > > Rich Freeman wrote: > > > > Out of curiosity, what model drive is it? Is it by chance an SMR / > > archive drive? > > Device Model: ST8000AS0003-2HH188 > > I recall reading about SMR but can't recall the details of what it is. > As far as I know, this is just a basic 8TB drive.
This is an SMR drive. You should DEFINITELY read up on what they are. For reads they're completely normal. For sequential writes to unused space they're completely normal. For random writes or overwrites they are significantly different from traditional hard drives. They work a bit like an SSD in the sense that blocks are arranged into larger erase regions. Within a region blocks can only be written sequentially. If you want to overwrite one block in the middle of a region, the drive will read the entire region into RAM, then write the entire region sequentially with the overwritten block to a new spot on the disk. This is just like in an SSD where if try to overwrite a block in a region with any unTRIMmed blocks the drive must read the entire region, erase the region, and write the modified region. Except that in an SSD those extra reads/writes operate with SSD access times. With an SMR drive those extra reads/writes operate with hard drive latencies, so they're MUCH more costly. For backup use they're usually fine, IF you're writing in a sequential file format that is appended to. If you're using rsync to do your backups then that isn't what you're doing and you're probably paying a heavy penalty. If you were doing incremental backups using tar/duplicity/whatever then you'd probably be fine. Some filesystems might be optimized for these drives to reduce the amount of overwriting in place. I haven't looked into it. I'd expect a log-based filesystem to work fairly well, though those can have high levels of fragmentation which is better suited for SSD than SMR. These drives all have fairly active firmware that manages this special overwrite process so that they can be used with operating systems that are naive to how they work. I wouldn't be surprised if this is what is causing the drive to be active after you unmount it. In theory it should be harmless to power it off. However, leaving it powered on probably will improve its performance as it can take care of any garbage collection before the next time you use it. If whatever journal it is using to speed things up gets full then you'll feel the full brunt of any write penalties until it is flushed. You might want to seriously consider changing to a backup format that just creates big tail-appended files containing incremental changes. Something like rsync that just outputs bazillions of little files is going to create lots of random writes when things change, vs consolidating all those changes into one file that just grows at the end. Treat them the way you would a tape (which is what tar was designed for). Nothing wrong with SMR drives per se - they can potentially be cheaper especially for backup (using an appropriate file format), and are just as fast for reading so they're also great for infrequently changing bulky data. However, random writes are very costly and you should be aware of that going in... -- Rich
