On 12/23/2016 01:03 PM, Greg Freemyer wrote:
Starting over on this topic.
While I wasn't looking HDDs got a major make-over and its a drastic change. This applies only to 5TB and bigger drives from what I can see at this point. And not all of those.
Anyway, I looked further into what makes a surveillance HDD different from other types. To my surprise, in the large disk (6/8/10 TB) market Seagate now offers:
- Archive HDDs - Surveillance HDDs (Skyhawk) - NAS HDDs (IronWolf) - Performance HDDs (Barracuda)
The reason seems to be they are incorporating SMR (shingled magnetic recording) storage tech.
This youtube video does what looks like a good explanation of SMR starting 4 minutes in: https://www.youtube.com/watch?v=CR_bfbOTY1o
But he doesn't explain that SMR isn't used on 100% of the platter. If it were done, half the entire drive would have to be rewritten with every write. ie. when a SMR sector is written it corrupts one of the sectors next to it. When you re-write the corrupted sector, it corrupts the next one, and before you're done fixing the corruptions you've rewritten half the drive to just write one sector in the middle of the drive.
Per http://www.anandtech.com/show/10470/the-evolution-of-hdds-in-the-near-future...
the new Seagate drives are interlacing SMR sections of the platter with traditional perpendicular recording. Every time a sector in a SMR region is written, the corruption in that entire SMR has to be fixed, but the corruption process ends at the edge of the particular SMR zone.
The "Archive HDDs" have highest ratio of SMR to perpendicular. In some cases a sector write can apparently take up to 20-seconds to complete because the SMR zones are so big and a write at the start of the zone would force a very large part of the SMR zone to be re-written.
For some (most? all?) SMR drives, they have a portion of the platter used as a write cache. Let's say 10GB of write cache, so when you write the first 10 GB of a data writing session, it goes straight to that write cache at tradional write speeds. Then when there is idle time the disk controller moves the data out to the much slower SMR regions.
So, Seagate is apparently tuning the ratio and configuration of SMR areas and perpendicular recording based on use cases.
The above youtube documents someone (like me) trying to use SMR drives not designed for RAID use in a raid array. The raid array apparently started kicking the SMR drives out of the array aggressively because of the very slow i/o speeds.
He got lucky and didn't have any data loss, but you clearly could if you're having too many drives kicked out of the array too quickly.
Hope that's informative, Greg
Wow. Talk about a fraud against the consumer marketed as feature. If a technology isn't ready for prime time, maybe it needs to age on the shelf for a few years before deployment. -- After all is said and done, more is said than done. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org