Different "geometries" for same disk model?

Submitted ⁨⁨10⁩ ⁨months⁩ ago⁩ by ⁨Hopfgeist@feddit.de⁩ to ⁨selfhosted@lemmy.world⁩

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

sd1 at scsibus0 target 1 lun 0:  disk fixed
sd1: 3726 GB, 348145 cyl, 10 head, 2244 sec, 512 bytes/sect x 7814037168 sectors

sd3 at scsibus0 target 3 lun 0:  disk fixed  
sd3: 3726 GB, 342419 cyl, 10 head, 2282 sec, 512 bytes/sect x 7814037168 sectors

sd7 at scsibus0 target 7 lun 0:  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.

source

Comments

Sort:hotnew top

Hopfgeist@feddit.de ⁨10⁩ ⁨months⁩ ago
I’m not touching that post again. But a small rant about typesetting in lemmy: It seems there is no way whatsoever to put angle brackets in a “code” section. In an overzealous amount to prevent HTML injection, everything in angle brackets is just removed when posting (although it remains there in preview). In normal text, you can use “<”, but not inside “code” segments, where it will be retained verbatim.

source
- tal@lemmy.today ⁨10⁩ ⁨months⁩ ago
  
  In an overzealous attempt to prevent HTML injection
  
  I think that they were actually getting hit with attacks.
  
  googles
  
  Yeah:
  
  lemmy.world/post/3986993
  
  Yeah I think this was hastily done to prevent the XSS injection attacks that were happening IIRC. They implemented encoding for content, but looks like they never got around to fully decoding it.
  
  source
taladar@sh.itjust.works ⁨10⁩ ⁨months⁩ ago
Maybe the larger disks have some sort of expected defective bits of the physical disks since it becomes increasingly difficult to produce flawless ones? Also, I am pretty sure ZFS didn’t even exist yet the last time anyone used cylinders/heads/sectors for anything. That is something from the parallel ATA era and not even close to the end of that.

source
- Hopfgeist@feddit.de ⁨10⁩ ⁨months⁩ 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.
  
  source