Originally Posted by jmbach
Yes the 1.7TB partition would be considered 4k aligned. Only if the disk I/O all occurs in that partition. That is the rub. How often the TiVo needs to access the root, kernel, swap, /var, and partitions 10 and 12 during operations is anybody's guess.
Based partially on the use of my ears (and sometimes a mechanic's stethoscope), the disk I/O in some of those partitions is intense, when in the process of indexing and GC. Let's just say that when using a drive with no AAM, and no "intelliseek", you can record all tuners concurrently, and not be able to hear much without a stethoscope, while nothing but your ears are required to tell when indexing and GC occur (and a stethoscope might damage your hearing during those processes).
I would almost wonder if the recent reports that the whole GC not completing issue, is verifiably only affecting larger than stock drives, could be helped by increasing the efficiency of the disk I/O, by reducing internal drive latency, thus reducing resources required to complete GC. Indexing and GC operations, although considered "background processes", are the most I/O intensive, seek intensive, and most susceptible to the issues AF drives brought into the equation, namely "Read-Modify-Write" operations, instead of just "Write" operations, as it would be on a native 512 byte sector drive.
An experiment I propose somebody try (with very good note keeping skills):
1. Find yourself having a TiVo, with an AF drive, that won't complete GC.
2. Clone the drive to a comparable native 512 byte sector drive of same size.
3. Run the clone, and see if GC completes, or completes more often.
4. Make sure nothing else was changed, that may have skewed result validity.
5. Clone in the reverse direction, and repeat #4.
6. Run the original drive, and see if GC completion is negatively affected.
7. Share all the details, notes, and results, with the rest of the class.
It's not a perfect test, and not everybody has a 512 byte sector native drive handy. But, if enough people try this, and the results are conclusive enough for plausibility of non-media partition disk I/O taking a hit on AF drives, enough to degrade Indexing and GC completion, then the importance of physical layout and alignment are made clear. Even if all that can be seen is a significant improvement in Indexing and GC completion times, that's noteworthy.
Since all drives have highest performance on the outer tracks, and follow a downward curve to the lowest performance on the inner tracks, the location of the databases, and other routinely processed non-AV data, with the highest random I/O demands (especially seek-intensive), would ultimately be placed strategically (not necessarily on the outermost tracks). The drives that are used in TiVos, and the ones most use to upgrade them, have good sequential performance. But, it literally falls off a cliff, from whatever sequential performance zone it is in, when it's non-sequential, and the drop starts from whatever point on the curve the drive would be at, if doing sequential operations.
Realistically, all drives should be able to handle the AV data that gets written to the Media partitions, no matter where it is on the platters, or if the media partitions are aligned, due to the large bulk writes. But, I'm not saying alignment has no value there (think fragmentation).
In summation, there's a reason why certain non-media partitions tend to be smack in the middle of the media partition pairs, and why they tend to come in pairs. There was a time when this was critical, then drive technology made it less so (via density and performance), then drive technology (via AF) seems to have made it just as important again, and it would be already clear, just how much, if large onboard drive cache wasn't camouflaging internal AF pitfalls (pulling the wool over our eyes).
If you have already upgraded, and don't have any issues, I don't advise starting over, unless the thought of making the drive work harder than it needs to, keeps you awake at night. If you are planning an upgrade, and want the drive to have the least workload overhead, then this stuff is for you.
Another potential performance-sapping drive technology that has somewhat invaded most modern drives (suspiciously around the advent of AF), is a replacement of AAM (where you could improve performance and have a louder drive, or have a quiet drive and lower seek performance, or set it somewhere in-between). WD's AAM replacement brand is "Intelliseek". These non-adjustable, and non-disableable seeking algorithms serve two purposes:
1. Quieter seeking (more of a secondary result).
2. Lower wear of the head actuator, and prevention of seek-errors, by preemptively timing seek operations, to make them less snap-action (and make them smoother), and attempt to lower the number of overall seeking operations, by consolidation and queuing of them, possibly even re-ordering them.
What they don't tell you, is that this technology increases latency internally, and is yet another feature that hides its pitfalls by using on-drive cache. I have no proof of this technology being a detriment, outside the drive. But, in theory, an unaligned drive, not optimally physically partitioned, just might overwhelm the processing capabilities for queuing up optimized seeks (drive optimized). I won't write a page worth of explaining how many different ways that could "go sideways".