Raid1 and macos

[latestmonkey]

Hi folks,

I currently back up everything manually (clone, time machine, important docs) but I'm looking for a more automated system so I'm thinking of buying a 2 disk enclosure like this one: http://www.amazon.com/Vantec-3-5-In...TF8&colid=369ZEBI6HEOFO&coliid=I2MW3RSR7IVNTX

But I don't understand how RAID1 works.

So let's say I put two 2TB drives in them, let's call them A and B.

Is it possible to partition these drives and RAID1 only certain partitions?

Ex:

A1 ----> B1
A2 ----> B2
A3 nomirroring B3

Also, does the enclosure do the mirroring or does OSX do the mirroring?

Sorry for dumb newbie questions.

Thanks

 

[switon]

Re: Raid 1...

Hi latestmonkey,

RAID 1, also known as "mirroring", does precisely that, it mirrors. In other words, when the OS wishes to write to a RAID 1 drive, the RAID 1 actually writes two copies simultaneously to two different volumes, typically on two different disks. This way there is a "built-in" backup, so if one of the two disks fails catastrophically, the chances are that the other drive is still working and thus you can recover your data from the working drive even after a failure of one drive.

Now this dual simultaneous writing is handled either by the RAID box itself (typically RAID boxes run a small version of a Linux kernel OS), or it can be done in software by the Mac OS when the Mac OS is used to setup the RAID 1 system.

Whether you can partition the two RAIDed drives into multiple partitions, some of which are not RAIDed, depends upon the actual system being used. I believe this is possible when doing software RAID, but most RAID boxes will not allow this, as their software will automatically use the entire disks for their RAID disks.

I would not recommend attempting to split up the disks into some RAIDed and some not RAIDed partitions anyway, as this is not an efficient use of the RAID system.

So, in a nutshell, either the Mac OS X does the RAID in software, or the RAID box does its own RAID in hardware or via using a small Linux kernel.

Regards,
Switon

 

[latestmonkey]

Hi latestmonkey,

RAID 1, also known as "mirroring", does precisely that, it mirrors. In other words, when the OS wishes to write to a RAID 1 drive, the RAID 1 actually writes two copies simultaneously to two different volumes, typically on two different disks. This way there is a "built-in" backup, so if one of the two disks fails catastrophically, the chances are that the other drive is still working and thus you can recover your data from the working drive even after a failure of one drive.

Now this dual simultaneous writing is handled either by the RAID box itself (typically RAID boxes run a small version of a Linux kernel OS), or it can be done in software by the Mac OS when the Mac OS is used to setup the RAID 1 system.

Whether you can partition the two RAIDed drives into multiple partitions, some of which are not RAIDed, depends upon the actual system being used. I believe this is possible when doing software RAID, but most RAID boxes will not allow this, as their software will automatically use the entire disks for their RAID disks.

I would not recommend attempting to split up the disks into some RAIDed and some not RAIDed partitions anyway, as this is not an efficient use of the RAID system.

So, in a nutshell, either the Mac OS X does the RAID in software, or the RAID box does its own RAID in hardware or via using a small Linux kernel.

Regards,
Switon

Thank you!

I'd prefer the box do the mirroring so as to not tax resources on my mbp.

Does anyone have a recommendation on a good one? I wouldn't mind having a NAS either.

 

[MCAsan]

The wiki entry for RAID has a good description of all the different RAID modes.

http://en.wikipedia.org/wiki/RAID

 

[switon]

RE: RAIDs...

Hi latestmonkey and MCAsan,


MCAsan: Thanks for the wikipedia link to RAID!

latestmonkey: I'll probably get chewed for this, but I would recommend that you look into the Synology DiskStations... Synology makes a number of RAID boxes having different numbers of bays and alternative connections including NAS. The Synology units also have a number of nice capabilities as well as offering various other software tools, including running a number of servers/services. Depending upon your needs, of course, you could also look at Drobo, G-Tech, Promise, WD, LaCie, etc. RAID units.

Regards,
Switon