I have one 1TB drive in addition to a 2TB drive. The 2TB drive is used by Time Machine. I'd like to add the 1TB to Time Machine's space. So I need Time Machine to back up to both drives. Is that possible? So my total backup space for Time Machine will be 3TB.
MacPro (Early 2008), Mac OS X (10.5.8), 2 x 2.8 Ghz Quad Core, 8GB RAM, ATI Radeon HD 2600
Only one backup drive at a time can be used. You can switch backup drives by changing the backup drive in TM preferences.
You can try creating a striped RAID array using Disk Utility and using the array as the backup destination. A striped array will give you the 3 TBs you want but it will appear to TM as a single backup device.
RAID Basics
For basic definitions and discussion of what a RAID is and the different types of RAIDs see RAIDs. Additional discussions plus advantages and disadvantages of RAIDs and different RAID arrays see:
RAID Array and Server: Hardware and Service Comparison.
Hardware or Software RAID?
RAID Hardware Vs RAID Software - What is your best option?
RAID is a method of combining multiple disk drives into a single entity in order to improve the overall performance and reliability of your system. The different options for combining the disks are referred to as RAID levels. There are several different levels of RAID available depending on the needs of your system. One of the options available to you is whether you should use a Hardware RAID solution or a Software RAID solution.
RAID Hardware is always a disk controller to which you can cable up the disk drives. RAID Software is a set of kernel modules coupled together with management utilities that implement RAID in Software and require no additional hardware.
Pros and cons Software RAID is more flexible than Hardware RAID. Software RAID is also considerably less expensive. On the other hand, a Software RAID system requires more CPU cycles and power to run well than a comparable Hardware RAID System. Also, because Software RAID operates on a partition by partition basis where a number of individual disk partitions are grouped together as opposed to Hardware RAID systems which generally group together entire disk drives, Software RAID tends be slightly more complicated to run. This is because it has more available configurations and options. An added benefit to the slightly more expensive Hardware RAID solution is that many Hardware RAID systems incorporate features that are specialized for optimizing the performance of your system.
For more detailed information on the differences between Software RAID and Hardware RAID you may want to read: Hardware RAID vs. Software RAID: Which Implementation is Best for my Application?
Only one backup drive at a time can be used. You can switch backup drives by changing the backup drive in TM preferences.
You can try creating a striped RAID array using Disk Utility and using the array as the backup destination. A striped array will give you the 3 TBs you want but it will appear to TM as a single backup device.
RAID Basics
For basic definitions and discussion of what a RAID is and the different types of RAIDs see RAIDs. Additional discussions plus advantages and disadvantages of RAIDs and different RAID arrays see:
RAID Array and Server: Hardware and Service Comparison.
Hardware or Software RAID?
RAID Hardware Vs RAID Software - What is your best option?
RAID is a method of combining multiple disk drives into a single entity in order to improve the overall performance and reliability of your system. The different options for combining the disks are referred to as RAID levels. There are several different levels of RAID available depending on the needs of your system. One of the options available to you is whether you should use a Hardware RAID solution or a Software RAID solution.
RAID Hardware is always a disk controller to which you can cable up the disk drives. RAID Software is a set of kernel modules coupled together with management utilities that implement RAID in Software and require no additional hardware.
Pros and cons Software RAID is more flexible than Hardware RAID. Software RAID is also considerably less expensive. On the other hand, a Software RAID system requires more CPU cycles and power to run well than a comparable Hardware RAID System. Also, because Software RAID operates on a partition by partition basis where a number of individual disk partitions are grouped together as opposed to Hardware RAID systems which generally group together entire disk drives, Software RAID tends be slightly more complicated to run. This is because it has more available configurations and options. An added benefit to the slightly more expensive Hardware RAID solution is that many Hardware RAID systems incorporate features that are specialized for optimizing the performance of your system.
For more detailed information on the differences between Software RAID and Hardware RAID you may want to read: Hardware RAID vs. Software RAID: Which Implementation is Best for my Application?
Thanks for the speedy response Kappy. When I go to Disk Utility and drag the 2 external drive icons into the RAID window, it seems I must choose "Concatatened" instead of "Striped" to get a RAID size of 3TB. Otherwise "Striped" is 2TB. Are you sure it would be "Striped"?
Yes, that's the same thing. "Concatenated" is used for a RAID array using non-matching drives. Also known as JBOD (Just a Bunch Of Disks.) Choose Concatenated.
BTW, both drives will be erased in the process, so once you create the array set it up as the TM backup device and let it perform a full backup.
I read that PDF comparing a software RAID (what I am doing I presume) and I'm a little spooked out from the disadvantages. I'm not so concerned about having a bootable volume from it, but those other things they mention such as OS migration, software crash and CPU usage. Any opinion on those things?
There are always potential concerns with any RAID. Of particular is that of drive failure. If a drive fails then all the array's data are lost. However, that isn't much different than having a single drive that fails. As a TM backup there are no issues associated with having a bootable backup since TM cannot provide a bootable backup, but for all other uses it would be fine. I have a mirrored RAID that I use for a backup and do not notice any problems with CPU usage.
Can Time Machine back up to 2 separate external drives?
