Any Disadvantages form SSD cache with Different size SSDs ?

 

i currently have a 120gig ssd (more like 111Gb)

and im expecting a 500gb one soon

 

is there any disadvantages or downfalls of using both in a ssd cache array ?

Any Disadvantages form SSD cache with Different size SSDs ?

Depends on what you mean by disadvantage.

Here is a calculator to show how much usable size you will end up having with any given combination.

http://carfax.org.uk/btrfs-usage/

Select the number of devices, RAID-1, and the size of each device. The total space for files will show you the usable capacity of any given combination of sizes.

is there anyway for me to use Raid0 them or just make a jbod ?

 

do i need to it in the bios (when i get my motherbored back) or can i do it form unraid ? #

 

something like a spanned volume ?

 

On the cache page type on the balance window:

 

For RAID0:

-dconvert=raid0 -mconvert=raid1

 

For Single (this is the only way to use all the space from different size sdds, equivalente to JBOD)

-dconvert=single -mconvert=raid1

 

Settings will survive a reboot but adding a new disk to pool sets it back to default (raid1).

... i currently have a 120gig ssd (more like 111Gb) ...

 

<Sigh>  I'm continually surprised at how much folks misunderstand disk sizes.    Disk drive manufacturers have always expressed their disk sizes in decimal units ... e.g. 1000 bytes is considered a kilobyte; 1,000,000 bytes is considered a megabyte, etc.    Computers speak "binary", where a KB is 2^10 (= 1024), a MB is 2^20 (1024 x 1024), etc.

 

So a 120GB disk will have 120,000,000,000 bytes, but your computer will show this as [120,000,000,000]/[1024 x 1024 x 1024] = 111.xx GB

 

It's not that your 120GB disk only has 111GB ... you're simply looking at two different ways of measuring the capacity.

 

... i currently have a 120gig ssd (more like 111Gb) ...

 

<Sigh>  I'm continually surprised at how much folks misunderstand disk sizes.    Disk drive manufacturers have always expressed their disk sizes in decimal units ... e.g. 1000 bytes is considered a kilobyte; 1,000,000 bytes is considered a megabyte, etc.    Computers speak "binary", where a KB is 2^10 (= 1024), a MB is 2^20 (1024 x 1024), etc.

 

So a 120GB disk will have 120,000,000,000 bytes, but your computer will show this as [120,000,000,000]/[1024 x 1024 x 1024] = 111.xx GB

 

It's not that your 120GB disk only has 111GB ... you're simply looking at two different ways of measuring the capacity.

 

I think the confusion is entirely because Hard Drive Manufacturers are using a system of measuring that works in their favor but isn't actually how computers work...

... i currently have a 120gig ssd (more like 111Gb) ...

 

<Sigh>  I'm continually surprised at how much folks misunderstand disk sizes.    Disk drive manufacturers have always expressed their disk sizes in decimal units ... e.g. 1000 bytes is considered a kilobyte; 1,000,000 bytes is considered a megabyte, etc.    Computers speak "binary", where a KB is 2^10 (= 1024), a MB is 2^20 (1024 x 1024), etc.

 

So a 120GB disk will have 120,000,000,000 bytes, but your computer will show this as [120,000,000,000]/[1024 x 1024 x 1024] = 111.xx GB

 

It's not that your 120GB disk only has 111GB ... you're simply looking at two different ways of measuring the capacity.

 

I think the confusion is entirely because Hard Drive Manufacturers are using a system of measuring that works in their favor but isn't actually how computers work...

I've even seen cases where <really big number> is divided by either 1000 or 1024, and then the resulting <still big number> is divided by either 1000 or 1024, with possibly a different choice for the divisor with each division. So you can get more than 2 answers that really mean the same thing.

Any Disadvantages form SSD cache with Different size SSDs ?

 

i currently have a 120gig ssd (more like 111Gb)

and im expecting a 500gb one soon

 

is there any disadvantages or downfalls of using both in a ssd cache array ?

Short is don't do that.

unRAID still does not support RAID 0 out of the box so you are likely to run into troubles.

 

Just mount either of the SSD out of array.

 

Btw, the notation is:

g = conventional giga = 10^9 (i.e. 1000 x 1000 x 1000)

G = computer giga = 2^30 (i.e. 1024 x 1024 x 1024)

b = bit (1/8 of a byte)

B = byte

 

So in your case, the notation is 120gB (or 111GB)

 

111Gb is 2^30 * 111 bit = 13.9 GB 

... i currently have a 120gig ssd (more like 111Gb) ...

 

<Sigh>  I'm continually surprised at how much folks misunderstand disk sizes.    Disk drive manufacturers have always expressed their disk sizes in decimal units ... e.g. 1000 bytes is considered a kilobyte; 1,000,000 bytes is considered a megabyte, etc.    Computers speak "binary", where a KB is 2^10 (= 1024), a MB is 2^20 (1024 x 1024), etc.

 

So a 120GB disk will have 120,000,000,000 bytes, but your computer will show this as [120,000,000,000]/[1024 x 1024 x 1024] = 111.xx GB

 

It's not that your 120GB disk only has 111GB ... you're simply looking at two different ways of measuring the capacity.

 

I think the confusion is entirely because Hard Drive Manufacturers are using a system of measuring that works in their favor but isn't actually how computers work...

I've even seen cases where <really big number> is divided by either 1000 or 1024, and then the resulting <still big number> is divided by either 1000 or 1024, with possibly a different choice for the divisor with each division. So you can get more than 2 answers that really mean the same thing.

 

interesting;

 

In December 1998, the IEC addressed such multiple usages and definitions by creating prefixes such as kibi, mebi, gibi, etc., to unambiguously denote powers of 1024.[11] Thus the kibibyte, symbol KiB, represents 210 = 1024 bytes. These prefixes are now part of the International System of Quantities. The IEC further specified that the kilobyte should only be used to refer to 1000 bytes. However, the kilobyte is still commonly used to refer to 1024 bytes.

 

(https://en.wikipedia.org/wiki/Kilobyte)

 

... i currently have a 120gig ssd (more like 111Gb) ...

 

<Sigh>  I'm continually surprised at how much folks misunderstand disk sizes.    Disk drive manufacturers have always expressed their disk sizes in decimal units ... e.g. 1000 bytes is considered a kilobyte; 1,000,000 bytes is considered a megabyte, etc.    Computers speak "binary", where a KB is 2^10 (= 1024), a MB is 2^20 (1024 x 1024), etc.

 

So a 120GB disk will have 120,000,000,000 bytes, but your computer will show this as [120,000,000,000]/[1024 x 1024 x 1024] = 111.xx GB

 

It's not that your 120GB disk only has 111GB ... you're simply looking at two different ways of measuring the capacity.

 

I think the confusion is entirely because Hard Drive Manufacturers are using a system of measuring that works in their favor but isn't actually how computers work...

 

It's my belief that the hard disk manufacturers are being honest but the RAM manufacturers have always been overly generous. The disk situation is further complicated by the file system overheads, which make users feel even more short-changed.

 

The prefixes kilo-, mega-, giga- and tera- mean multiples of 10 in all other contexts so why should data storage be different? That's why the binary prefixes kibi- (ki), mebi- (Mi), gibi- (Gi) and tebi (Ti) were introduced. I'm not sure about Windows but the recent releases of OS X get the numbers correct but are vague on the units, while most Linux desktops get the units correct as well.

 

So it's really just laziness that makes us say "32 GB of RAM and a 6 TB hard disk" when we should say "32 GiB of RAM and a 6 TB hard disk", but then a lot of people even struggle with the difference between a bit (b) and a byte (B).

 

EDIT: Ah, the joys of near simultaneous posting!

 

g = conventional giga = 10^9 (i.e. 1000 x 1000 x 1000)

G = computer giga = 2^30 (i.e. 1024 x 1024 x 1024)

 

No. Not true. G = giga- = 10⁹

 

Regardless of attempts to modify the terminology, the "disk-maker-ese" vs. "computerese" difference in what a KB, MB, GB, etc. mean have been exactly the same for as long as I can remember ... and I've been dealing with these for over 50 years.

 

The simple fact is it's not likely to ever change in common usage ... but new users will likely always think they're getting disks that don't have as much as the advertised capacity when they buy a X terabyte disk and Windows reports it as something less.  For example, this is from a 3TB disk (Note that it does have over 3,000,000,000,000 bytes, but shows 2.72TB as the size) ...

 

So Windows is still doing it wrong, which was really my point. OS X does it better:

On the other hand, OS X gets it wrong when dealing with RAM. So that makes it inconsistent too, which annoys me.

... So Windows is still doing it wrong ...

 

Not at all.  The inconsistency between "computerese" and "disk-driver-maker-ese" in the meaning of a KB (MB, GB, TB, etc.) has been exactly the same since they first started making disk drives over half a century ago.    This difference was evident in the early computers from all manufacturers ... IBM, Univac, etc.    I first encountered this in an IBM 7040 ~ 1961, and the same distinction was evident in very system I've ever worked with ... from IBM, Cray, DEC, Univac, etc. => LONG before the advent of personal computers or Microsoft.

 

I think we're going to have to agree to differ on this one, Gary I agree, though, that there's an inconsistency between "computerese" and "disk-driver-maker-ese", as you call them, but my opinion is that it's the RAM manufacturers and Microsoft and Apple (partly) that have it wrong. The disk manufacturers and most Linux desktops and Apple (partly) have it right.