this post was submitted on 13 Nov 2023
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Different "geometries" for same disk model? (feddit.de)
submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/[email protected]
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I know that for decades now, hard disks don't really reveal their actual internal geometry (which is complicated anyway, since inner cylinders may have fewer sectors than outer cylinders, etc.), and present fictional geometries to satisfy legacy software, but I found it weird anyway.

I have a ZFS raidz2 NAS which originally consisted of 8x2 TB SAS disks and is now in the process of being live-upgraded to 8x4 TB (change disks one by one, resilver, change, resilver, etc ...)

I now have four of the disks replaced, and in NetBSD they all report different geometries. They all report the exact same number of total blocks, so it's not actually an issue, but still strange.

sd0 at scsibus0 target 0 lun 0: <SEAGATE, ST4000NM0023, GE11> disk fixed

sd0: 3726 GB, 330809 cyl, 10 head, 2362 sec, 512 bytes/sect x 7814037168 sectors

sd1 at scsibus0 target 1 lun 0: <SEAGATE, ST4000NM0023, GE11> disk fixed

sd1: 3726 GB, 348145 cyl, 10 head, 2244 sec, 512 bytes/sect x 7814037168 sectors

sd3 at scsibus0 target 3 lun 0: <IBM-B040, ST4000NM0023, BC5P> disk fixed

sd3: 3726 GB, 342419 cyl, 10 head, 2282 sec, 512 bytes/sect x 7814037168 sectors

sd7 at scsibus0 target 7 lun 0: <IBM-B040, ST4000NM0023, BC5P> disk fixed

sd7: 3726 GB, 341874 cyl, 10 head, 2285 sec, 512 bytes/sect x 7814037168 sectors

Two of them are IBM-branded (although they are in fact all Seagate Constellation ES.3), so I might expect slight differences, but even those with the same branding and the same revision present different geometries.

Anyway, probably just a curiosity, it will be interesting to find what the remaining four disks will show.

I might add that the older 2 TB disks (Seagate Constalleation ES, IBM-branded) all show the exact same geometry:

sd2 at scsibus0 target 2 lun 0: <IBM-ESXS, ST32000444SS, BC2D> disk fixed

sd2: 1863 GB, 249000 cyl, 8 head, 1961 sec, 512 bytes/sect x 3907029168 sectors

sd4 at scsibus0 target 4 lun 0: <IBM-ESXS, ST32000444SS, BC2D> disk fixed

sd4: 1863 GB, 249000 cyl, 8 head, 1961 sec, 512 bytes/sect x 3907029168 sectors

sd5 at scsibus0 target 5 lun 0: <IBM-ESXS, ST32000444SS, BC2D> disk fixed

sd5: 1863 GB, 249000 cyl, 8 head, 1961 sec, 512 bytes/sect x 3907029168 sectors

sd6 at scsibus0 target 6 lun 0: <IBM-ESXS, ST32000444SS, BC2D> disk fixed

sd6: 1863 GB, 249000 cyl, 8 head, 1961 sec, 512 bytes/sect x 3907029168 sectors

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[–] [email protected] 1 points 1 year ago* (last edited 1 year ago)

Sure, SCSI disks will show their defective list ("primary defects", as delivered by the factory, and grown defects, accumulated during use), and they all have a couple hundred primary defects. But I don't see why that would affect the reported geometry, given that it is fictional, anway. And all disks have enough spare tracks to accommodate for the defects, and offer the specified full number of total sectors, even for long list of grown defects. Incidentally, all the 4TB disks are still "perfect" in that they have no grown defects.

And yes, ever since LBA, nobody has used sectors and cylinders for anything.