Will the real 4TB drive please stand up...

[PattyTeacher]

I have three 4TB drives.  Seagate, Western Digital, Toshiba.

Even though they are all labeled/sold as "4TB drives"... they are each probably slightly different sizes around 3.6TB or 3.7TB as "usable space".

I want to use 1 of them as a parity drive.  

 

What's the easiest way to find the largest one?  Or does it really not matter since they are all labeled 4TB?

Can a drive that is 0.001% smaller be used as a parity drive for a one that is 0.001% larger than it?

Can I trust the manufacture's "claimed true size"?

 

[JorgeB]

24 minutes ago, PattyTeacher said:

they are each probably slightly different sizes around 3.6TB or 3.7TB as "usable space".

No, they all will have the same exact capacity, brand/model doesn't matter, except some drives that come from USB enclosures.

[PattyTeacher]

> No, they all will have the same exact capacity, brand/model doesn't matter, except some drives that come from USB enclosures.

 

I'm not sure how all manufacturers in the world, for all the drive models, would all make them *EXACT* the same size for all their 4TB drives.

All the same number of platters, all the same number of sectors, all the same 'bytes per sector', same storage density, all CMR, all SMR, etc.

I'm sure "some" would be a few bytes (or kbytes) bigger or smaller.

 

I have no idea why the same drive put "inside" a computer, would be a different size than the ones they put into "external cases".

Do they have totally different assembly-lines making "drives for inside computers" VS "drives for external cases"?

Edited December 13, 2021 by PattyTeacher

[PattyTeacher]

> Look through the syslog, it should indicate the device names and exact sizes. Though that information is available through the UI dashboard too.

 

What's the easiest/quickest way to find the syslog?

 

I don't see it anywhere in the UI dashboard.  It's best to tell *HOW* to find something... not just "go find it.... it'll be there".

Where?

[JorgeB]

2 minutes ago, PattyTeacher said:

I'm sure "some" would be a few bytes (or kbytes) bigger or smaller.

They are not, they have the same exact number of sectors, at lest for the last decade or so, this is certainly on purpose, or you could get into trouble replacing disks for e.g. RAID arrays.

[JonathanM]

44 minutes ago, PattyTeacher said:

I'm not sure how all manufacturers in the world, for all the drive models, would all make them *EXACT* the same size for all their 4TB drives.

All the same number of platters, all the same number of sectors, all the same 'bytes per sector', same storage density, all CMR, all SMR, etc.

I'm sure "some" would be a few bytes (or kbytes) bigger or smaller.

For the last 20 years or so, drives have been addressed not by physical cylinders heads and sectors (CHS), but by logical block addresses (LBA). This means that when the OS asks to store and retrieve data, it's no longer referencing a physical spot on the drive directly like MFM and RLL did. All modern drives have varying amounts of real physical space like you said, but they are all presented with an industry standard size available to the OS. They use the excess space as spares, or to enhance performance, or whatever the manufacturer decides.

 

The result is that all modern internal interface drives present the exact same addressable space to the OS, and the old practice of writing bad sectors on the top of the drive in sharpie so you could tell the controller which addresses to avoid is all handled automatically in the firmware. ALL hard drives have bad sectors from the factory at the hardware level, but appear perfect to the OS because they are remapped. They also have automatic handling of sectors that are damaged or go bad during the lifetime of the drive, so as long as the remapping function has enough spare sectors left, the drive will keep the appearance of being error free to the OS, while triggering SMART alerts as the spare sector pool is used up.

[wgstarks]

19 hours ago, PattyTeacher said:

What's the easiest/quickest way to find the syslog?

Tools>System Log