maybe a silly RAID question

phyrexia

macrumors 6502a
Original poster
Sep 3, 2010
611
0
Ok, it's late. Level with me here.

I recently installed a Samsung 470 SSD (256gb) into my laptop (17" 2011). I wonder if the following is possible:

1. Buy another identical SSD, install it in the optical bay (to replace my stock 750gb HDD)
2. Partition both drives in half (128gb/128gb in my case, so four 128gb partitions in total)
3. Create one RAID 1 array/mirror with two of the 128gb partitions (one on each disc)
4. Create one RAID 0 array/striped with the other two 128gb partitions

thus creating a mirrored 128gb array for the OS and applications and another 256gb array for storage and whatnot?

Just thinking aloud.
 

JasonH42

macrumors 6502
Feb 9, 2010
310
11
you can't make raid with partitions,
Er, yes you can - that's how it works. You create partitions and add them to RAID volumes. I have a couple of small FAT partitions on my twin SSDs for Windoze (since it can't work with OSX software RAID for obvious reasons) and a large partition on each configured as one big OSX RAID0 volume.

Bear in mind that SATA III SSDs simply don't work in the optical bay of 15" and 17" MBPs reporting 6Gbps connection speed there. If you have a 13" MBP you'll be fine however. If your MBP reports 3Gbps in the optical bay then your RAID volumes will only run at 3Gbps and so there isn't much point running RAID0.
 

HellDiverUK

macrumors 6502
Oct 24, 2009
460
0
Belfast, UK
You can't make a RAID out of partitions. If you think you have, you're wrong, you haven't.

RAID - Redundant Array (of) Inexpensive Disks.

The hint's in the name. :rolleyes:

You can however, partition on a RAID volume. So you'd have a 256GB RAID1 array of two SSDs, then split that in half for two 128GB partitions. But you can't do what the OP is wanting to do and split the drive in to two partitions and RAID the partitions.
 

maflynn

Moderator
Staff member
May 3, 2009
66,710
33,603
Boston
But you can't do what the OP is wanting to do and split the drive in to two partitions and RAID the partitions.
Not only RAID the partitions but RAID them different. As others mentioned, RAID is at the physical disk level, not partition level.
 

trikky

macrumors regular
Nov 10, 2011
225
1
Ok, it's late. Level with me here.

I recently installed a Samsung 470 SSD (256gb) into my laptop (17" 2011). I wonder if the following is possible:

1. Buy another identical SSD, install it in the optical bay (to replace my stock 750gb HDD)
2. Partition both drives in half (128gb/128gb in my case, so four 128gb partitions in total)
3. Create one RAID 1 array/mirror with two of the 128gb partitions (one on each disc)
4. Create one RAID 0 array/striped with the other two 128gb partitions

thus creating a mirrored 128gb array for the OS and applications and another 256gb array for storage and whatnot?
My personal opinion is that this is a bad setup. Most likely it's going to be the drive itself that goes bad, not the partition. Relying on partitions for your RAID backup could lead to problems.
 

JasonH42

macrumors 6502
Feb 9, 2010
310
11
You can't make a RAID out of partitions. If you think you have, you're wrong, you haven't.

RAID - Redundant Array (of) Inexpensive Disks.

The hint's in the name. :rolleyes:

You can however, partition on a RAID volume. So you'd have a 256GB RAID1 array of two SSDs, then split that in half for two 128GB partitions. But you can't do what the OP is wanting to do and split the drive in to two partitions and RAID the partitions.
I guess my MBP doesn't exist then. Do you all work at the Genius bar? :D

Remember this is software RAID...
 

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phyrexia

macrumors 6502a
Original poster
Sep 3, 2010
611
0
Funny thread.

Thanks everyone, for playing along with my thought experiment.

I was under the impression you could (for example) take an 80GB disc and a 100GB disc and RAID1 the two together by only using 80gb of the larger disc (thus, RAID with partitions).

At least, the wikipedia article on RAID leads me to that conclusion.

http://en.wikipedia.org/wiki/Standard_RAID_levels said:
Such an array can only be as big as the smallest member disk.
 

JasonH42

macrumors 6502
Feb 9, 2010
310
11
Funny thread.

Thanks everyone, for playing along with my thought experiment.

I was under the impression you could (for example) take an 80GB disc and a 100GB disc and RAID1 the two together by only using 80gb of the larger disc (thus, RAID with partitions).

At least, the wikipedia article on RAID leads me to that conclusion.
You can in my imaginary world (with screenshot!) because it is software RAID...
 
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