This is a deepish dive so feel free to give the convo a miss (^-^)
But there is one VERY important aspect SMR users need to know IMO.
I understood the basic principles behind SMR (Shingled Magnetic Recording) drives, but hadn't given much thought to the actual implementation. I recently watched this VERY informative presentation that IMO is well suited to audiences like us.
Despite recommendations to not run Level 3+ on SMR drives, many users might not even know they have them. Even the 34 page manual for my Seagate ST8000AS002 simply states "TGMR recording technology provides the drives with increased areal density" ...indeed
The inner workings of SMR drives may be beyond the scope of SR 6.1, but I think it's still helpful to know (or speculate) what's happening.
Unless otherwise informed, I'm assuming SR 6.1 is 'SMR unaware'.
For level 2, how does the recovery differ between "band data" and "cache data"? What happens after the recovered data is written to the persistent
cache? Does Spinrite verify what it just wrote from the cache or the band? What are the implications of bands having to be rewritten in their entirety when you change even 1 bit? How are bad sectors mapped in the cache? Are entire bands mapped out if there is a defect anywhere within?
**The really important part**
I have experimented with levels 3-5, and observed behaviour consistent with the persistent cache explained in the above video. In short, ALL data is written to the persistent cache first. Only then is it transferred to the appropriate band. The drive will wait for a few seconds of idle time before transferring data from cache to band. Or if the cache is full, the drive will interrupt further input until it can clear some space.
The bottom line is that while Spinrite's initial read is from a "band track", I think ALL subsequent write/read/verify is done ONLY on the persistent cache. The only way to verify the 'permanent data' is to somehow flush the cache before reading back what was just written. Or work in timed intervals to give the cache time to write everything out before verifying.
I did not record any figures or make calculations. But I did observe that after pausing Spinrite, I could feel the heads continue sweeping back&forth for several minutes. A clear indication the drive was busy transferring data from persistent cache to data bands. When the heads went still, I'd unpause spinrite and let it get on with its work. The time remaining would drop, then start climbing again when the cache filled up.
Given the persistent cache is 10's of gigabytes, I imagine even SR level 5 does all of its flipping, writing and verifying there entirely, completely unaware it's not touching the data's permanent location on the bands.
Level 3 can be useful for refreshing the bits on the media, but as I understand it levels 4 & 5 should absolutely be avoided. They work the drive so hard there's a real possibility of some data corruption. And level 5's final verification would give a false sense of security as it's more likely reading from the media cache instead of the band.
Whew, this went longer than I expected
. Well anyway just happy to share my findings with anyone that might be interested. And if anything here can inform Spinrite 7 development so much the better.
But there is one VERY important aspect SMR users need to know IMO.
I understood the basic principles behind SMR (Shingled Magnetic Recording) drives, but hadn't given much thought to the actual implementation. I recently watched this VERY informative presentation that IMO is well suited to audiences like us.
Despite recommendations to not run Level 3+ on SMR drives, many users might not even know they have them. Even the 34 page manual for my Seagate ST8000AS002 simply states "TGMR recording technology provides the drives with increased areal density" ...indeed
The inner workings of SMR drives may be beyond the scope of SR 6.1, but I think it's still helpful to know (or speculate) what's happening.
Unless otherwise informed, I'm assuming SR 6.1 is 'SMR unaware'.
For level 2, how does the recovery differ between "band data" and "cache data"? What happens after the recovered data is written to the persistent
cache? Does Spinrite verify what it just wrote from the cache or the band? What are the implications of bands having to be rewritten in their entirety when you change even 1 bit? How are bad sectors mapped in the cache? Are entire bands mapped out if there is a defect anywhere within?
**The really important part**
I have experimented with levels 3-5, and observed behaviour consistent with the persistent cache explained in the above video. In short, ALL data is written to the persistent cache first. Only then is it transferred to the appropriate band. The drive will wait for a few seconds of idle time before transferring data from cache to band. Or if the cache is full, the drive will interrupt further input until it can clear some space.
The bottom line is that while Spinrite's initial read is from a "band track", I think ALL subsequent write/read/verify is done ONLY on the persistent cache. The only way to verify the 'permanent data' is to somehow flush the cache before reading back what was just written. Or work in timed intervals to give the cache time to write everything out before verifying.
I did not record any figures or make calculations. But I did observe that after pausing Spinrite, I could feel the heads continue sweeping back&forth for several minutes. A clear indication the drive was busy transferring data from persistent cache to data bands. When the heads went still, I'd unpause spinrite and let it get on with its work. The time remaining would drop, then start climbing again when the cache filled up.
Given the persistent cache is 10's of gigabytes, I imagine even SR level 5 does all of its flipping, writing and verifying there entirely, completely unaware it's not touching the data's permanent location on the bands.
Level 3 can be useful for refreshing the bits on the media, but as I understand it levels 4 & 5 should absolutely be avoided. They work the drive so hard there's a real possibility of some data corruption. And level 5's final verification would give a false sense of security as it's more likely reading from the media cache instead of the band.
Whew, this went longer than I expected
. Well anyway just happy to share my findings with anyone that might be interested. And if anything here can inform Spinrite 7 development so much the better.
