How to check for matching USB flash drive sizes?

[xyzzy]

I understand that manufacturers of USB flash drives will sometimes make tiny changes in capacity for a given model during the product lifecycle.

If I want to mirror the USB boot device and have a spare for future use, is there an easy way or a tool to reliably check that the USB flash drives I've got are exact matches, size-wise?

Thanks!

 

[Ericloewe]

If you want to be absolutely safe, you can install to all three drives and then remove one and wipe it.

 

[dtom10]

It does not matter, a mirror uses the smallest size available. You'll end up with a mirror and some spare Kb/Mb on the larger drive. The FS will have the same size on both drives.

A spare is pointless, just make sure you have the proper config. In case of a failure you install from scratch and restore the matching config. E.G.: install Freenas 9.10 for a 9.10 config or Freenas 11-U2 for a Freenas 11-U2 config.

 

[danb35]

It does not matter, a mirror uses the smallest size available.

It does matter, because if the designated spare is smaller than the other two, FreeNAS/ZFS will refuse to add it as a mirror. Though I agree that a spare really isn't necessary anyway.

 

[xyzzy]

Thanks to everyone for their feedback.

danb35 hit on exactly the problem I wanted to avoid.

While Ericloewe's approach would certainly work, here's another:

1) Zero out the boot sector using a tool like ImageUSB
2) Start Rufus and click on the "Log" button. It will show something like this:

Code:

Found USB 2.0 device 'SanDisk Ultra Fit USB Device' (0781:5583)
NOTE: This device is an USB 3.0 device operating at lower speed...
1 device found
No volume information for drive 0x85
Disk type: Removable, Sector Size: 512 bytes
Cylinders: 3738, TracksPerCylinder: 255, SectorsPerTrack: 63
Partition type: SFD (Super Floppy Disk) or Unpartitioned
Partition 0:
  Type: Small FAT16 (0x00)
  Size: 28.6 GB (30752636928 bytes)
  Start Sector: 0, Boot: No

The byte count in the 2nd to last line appears to be reliable. I just bought 4 SanDisk Ultra Fit drives and they all have this size. I compared it to one I bought 8 months ago, and it has a size of 30752000000 bytes.