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View Full Version : How many hard disks can be attached to a Macintosh System?


naveen
Nov 25, 2004, 05:54 AM
hi all
I want to know that How many hard disks can i attach to a Macintosh System?
Plz tell me the extreme limit?

Thanks and Regards

robbieduncan
Nov 25, 2004, 07:33 AM
To all intents and purposes it's infinite! You are basically limited by what the busses will support. So on a PowerMac G5 (for example) you have space (and SATA channels) for 2 disks. In addition you can attack discs to the USB and FireWire buses. A USB bus can support up to 127 devices, all of which can be disks (assuming you have a boat load of hubs). iirc each port is on it's own bus so you can hang 127 disks off each USB port. Of course this would be a bad idea as all the disks would share the bandwidth. I'm not sure what the single bus limit for FireWire is, but I think it's similar to USB.

wrldwzrd89
Nov 25, 2004, 08:27 AM
To all intents and purposes it's infinite! You are basically limited by what the busses will support. So on a PowerMac G5 (for example) you have space (and SATA channels) for 2 disks. In addition you can attack discs to the USB and FireWire buses. A USB bus can support up to 127 devices, all of which can be disks (assuming you have a boat load of hubs). iirc each port is on it's own bus so you can hang 127 disks off each USB port. Of course this would be a bad idea as all the disks would share the bandwidth. I'm not sure what the single bus limit for FireWire is, but I think it's similar to USB.
The FireWire bus limit is 63, with an additional limit of 16 devices in one daisy chain.

Jo-Kun
Nov 25, 2004, 08:33 AM
take the G5, you get 2 SATA bays (max 400GB/disk for now) you can add 2 SATA drives with for instance the G5jam (lose the first of the PCI slots) then you can add disks onto the USB2.0 ports (combined with hubs and so...) then you have both the FW400 & 800 ports... kill them to the fullest... get another PCI USB/FW card-> lose one more slot & add a lot more drives... if you're not broke then, get a fibrechannel card and an Xserve Raid ... ok by now you schould be broke, have a lot of storage, so ow we come to the final question: will you need this much drives/storage??? will you be able to max out your mac and still be in the need of more storage???

I think this was a silly question ;-)

-edit-
hmm

just been thinking: take the G5 put 2 SATA 400GB drives inside, buy 3 5,6TB Xserve Raids + the pcicards (17,6TB so far)
then we will max out the FW ports (2x FW400 + 1xFW800) someone mentioned: 16 devices/port = 48, ok we buy 48 1,6TB BiggerDisks (another 76,8TB)
then we have our USB2 channel (we don't care about speed decrease, its all about how much ;-) ) with the number stated here (being 127) and get a lot of hubs :-S and buy 1TB triple interface Bigger disks (127 of them -> 127TB)

well we end up with 221,4 TB hmm I think that's enough ;-)

-edit-
-edit2-
when buying FW hubs... we can increase the total of drives to 189 (302,4TB) so theoretically we now come to 430,2 TB

so I can state: you will never out max your Mac, so don't worry, enough expansion here ;-)

-edit2-

wrldwzrd89
Nov 25, 2004, 10:32 AM
take the G5, you get 2 SATA bays (max 400GB/disk for now) you can add 2 SATA drives with for instance the G5jam (lose the first of the PCI slots) then you can add disks onto the USB2.0 ports (combined with hubs and so...) then you have both the FW400 & 800 ports... kill them to the fullest... get another PCI USB/FW card-> lose one more slot & add a lot more drives... if you're not broke then, get a fibrechannel card and an Xserve Raid ... ok by now you schould be broke, have a lot of storage, so ow we come to the final question: will you need this much drives/storage??? will you be able to max out your mac and still be in the need of more storage???

I think this was a silly question ;-)

-edit-
hmm

just been thinking: take the G5 put 2 SATA 400GB drives inside, buy 3 5,6TB Xserve Raids + the pcicards (17,6TB so far)
then we will max out the FW ports (2x FW400 + 1xFW800) someone mentioned: 16 devices/port = 48, ok we buy 48 1,6TB BiggerDisks (another 76,8TB)
then we have our USB2 channel (we don't care about speed decrease, its all about how much ;-) ) with the number stated here (being 127) and get a lot of hubs :-S and buy 1TB triple interface Bigger disks (127 of them -> 127TB)

well we end up with 221,4 TB hmm I think that's enough ;-)

-edit-
-edit2-
when buying FW hubs... we can increase the total of drives to 189 (302,4TB) so theoretically we now come to 430,2 TB

so I can state: you will never out max your Mac, so don't worry, enough expansion here ;-)

-edit2-
It's not 16 per port, it's 16 per chain. That means that devices before a branch in the daisy chain count towards the limit for all chains connected to them, whereas devices after a branch count only toward that branch's 16 device limit. This means that a configuration like this would be perfectly legal:


CPU
|
1--2--3--4--5--6--7--8--9--10-11-12-13-14-15-16
| | | | | | | | | |
62 53 45 38 32 27 23 20 18 17
| | | | | | | | |
63 54 46 39 33 28 24 21 19
| | | | | | |
55 47 40 34 29 25 22
| | | | | |
56 48 41 35 30 26
| | | | |
57 49 42 36 31
| | | |
58 50 43 37
| | |
59 51 44
| |
60 52
|
61

Mechcozmo
Nov 25, 2004, 12:48 PM
2 per ATA bus, 1 per SATA bus. But with a PCI card... a helluva of a lot more.

SCSI is up to 15 I think, per bus.

Mord
Nov 25, 2004, 12:57 PM
so thats 2 extra drives on the optical drive bus

and everyone dont forget haveing racks and racks of xserve raids being connected via the gigabit ethernet

Mechcozmo
Nov 25, 2004, 02:57 PM
and everyone dont forget haveing racks and racks of xserve raids being connected via the gigabit ethernet

Yup, each one with its own drive controller... :D

Basically, you can keep on going...and going... and going... until the filesystem cannot encode any more but that is somewhere around 16 TB I think, or maybe 32 TB... a hell of a lot of songs in iTunes!

gekko513
Nov 25, 2004, 03:29 PM
So, externally, you have essentially unlimited storage.

Internally it's ready for two drives for a total of 800GB. It's possible to mount two extra drives internally if you're willing to mod it a little.

trailblazer
Nov 25, 2004, 03:38 PM
dont forget all the space you'd loose to formatting :D

Sun Baked
Nov 25, 2004, 04:13 PM
If the space on the desk isn't too big...

How Big is your wallet?

Let's see, three free PCI-X slots means 3 Fibre Channel cards (@ $499 = $1500)

With 3 5.6TB XServe Raid Units (@ $12,999 = $39,000).

So for about $45000 you can add 16,800 GB on 42 drives to your computer in a compact space using these...

http://a248.e.akamai.net/7/248/2041/664/store.apple.com/Catalog/US/Images/productshotxserveraid.jpg

At which point it would probably be a good idea to be running Mac OS X Server with XSan on some XServes for redundancy.

Jo-Kun
Nov 26, 2004, 03:35 AM
dont forget all the space you'd loose to formatting :D

no DO forget, its nicer when bragging about your way to expensive system of storage you will not be needing ;-)

and with this much storage I think you'll better buy one of these server racks to reduce space of your external storage system, and don't worry if you want to spend your money on FW/USB drives, you can convert LaCie's D2 series into a rackmount solution ;-)

Makosuke
Nov 26, 2004, 08:02 AM
Odd question, amusing answers. I wonder if there's a limit to the number of logical volumes OSX can address? I assume there is, though it's no doubt quite high. I know the max size for an individual HFS+volume is somewhere in the exabyte range (8EB?), so that's another limit to consider if you're getting theoretical.

dont forget all the space you'd loose to formatting :DActually, do forget, because it's not that much; unless I'm quite mistaken, most of the space "lost" between quoted capacity (say, 120GB) and formatted capacity (say, 112GB) is not due to the format, which only takes a few MB, but the fact that the OS calculates drive size in a different way than the drive manufacturerers.

Manufacturers calculate 1GB = 1,000,000,000 bytes, where for some archaic reason most major OSes calculate 1GB = 1024bytes/KB X 1024KB/MB X 1024MB/GB = 1,073,741,824 bytes. These "OS Gigabytes" are also sometimes called Gibibytes.

So a 120GB drive has 120 / 1.073 = 111.75GB of space according to the OS.

Les Kern
Nov 26, 2004, 08:32 AM
...unless I'm quite mistaken, most of the space "lost" between quoted capacity (say, 120GB) and formatted capacity (say, 112GB) is not due to the format, which only takes a few MB, but the fact that the OS calculates drive size in a different way than the drive manufacturerers.

I thought it was because the OS had to draw the "lines in the empty parking lot so the cars would know where to park". (My own metaphor)
So in a 120 GB drive it needed about 8 GB for the formatted directory. Please clear this up because I hate when I believe a lie for so long!

wrldwzrd89
Nov 26, 2004, 08:34 AM
Odd question, amusing answers. I wonder if there's a limit to the number of logical volumes OSX can address? I assume there is, though it's no doubt quite high. I know the max size for an individual HFS+volume is somewhere in the exabyte range (8EB?), so that's another limit to consider if you're getting theoretical.

Actually, do forget, because it's not that much; unless I'm quite mistaken, most of the space "lost" between quoted capacity (say, 120GB) and formatted capacity (say, 112GB) is not due to the format, which only takes a few MB, but the fact that the OS calculates drive size in a different way than the drive manufacturerers.

Manufacturers calculate 1GB = 1,000,000,000 bytes, where for some archaic reason most major OSes calculate 1GB = 1024bytes/KB X 1024KB/MB X 1024MB/GB = 1,073,741,824 bytes. These "OS Gigabytes" are also sometimes called Gibibytes.

So a 120GB drive has 120 / 1.073 = 111.75GB of space according to the OS.
If you see that "Gibibytes" are derived from binary (since 2^10=1024, and 1024 is as close to 1000 as you can get in exact powers of 2), then "OS Gigabytes" aren't archaic at all - rather, they're represented that way because computers don't know what base 10 (our decimal system) is - all they know is base 2 (binary, or 0's and 1's).

EDIT:
Les Kern:
Computers count everything in binary terms (0's and 1's); we use decimal terms (0 through 9). Therefore, rough equivalents like 1000=1024 have been made to "simplify" things for those of us who don't understand binary. Unfortunately, those "rough equivalents" are the same reason why formatted capacity and quoted capacity differ so much - those little inaccuracies in the equivalencies add up as the scale increases.

wrldwzrd89
Nov 26, 2004, 08:51 AM
Here's an analysis of the inaccuracy of the rough equivalency 1000=1024 at different scales:

At a scale of 1 (bytes), the equivalency is not applicable.
At 1000 (kilobytes), it over-estimates by 24 bytes.
At 1,000,000 (megabytes), it over-estimates by 48,576 bytes.
At 1,000,000,000 (gigabytes), it over-estimates by 73,741,824 bytes.
At 1,000,000,000,000 (terabytes), it over-estimates by 99,511,627,776 bytes.

All of these error values need to be multiplied by the size of the disk in question (and converted to the appropriate scale). To convert bytes to kilobytes, divide by 1024. Bytes to megabytes: divide by 1024^2. Bytes to gigabytes: divide by 1024^3. Bytes to terabytes: divide by 1024^4.

These error values were computed using the following method:

Scale values (SV):
0=bytes 1=kilobytes 2=megabytes 3=gigabytes 4=terabytes etc.

1024^SV - 1000^SV

gekko513
Nov 26, 2004, 12:02 PM
I thought it was because the OS had to draw the "lines in the empty parking lot so the cars would know where to park". (My own metaphor)
So in a 120 GB drive it needed about 8 GB for the formatted directory. Please clear this up because I hate when I believe a lie for so long!
I'm sorry but it's true that 1GB HD style = 0.93GB OS style and it's correct as they say in this thread that the OS uses gibibytes (giga binary bytes) which is 2^30 = 1.0737 GB.

The OS also has to draw lines in the empty parking lot, but that is only half the reason why harddrives "lose" so much capacity when viewed by an OS.

Sun Baked
Nov 26, 2004, 12:32 PM
It's 16800 GB in three drive enclosures, I think you can afford a MB here or there for the File System and the marketing teams hot air. ;)