[Reggie Fowler]

In anticipation of getting a new MacPro in the next week or two, i thought now would be the time to ask the following question:

I know the benefit of using Raid 1 (carbon copy) on one of my drives. Sure, its a secure way of having a backup, as it copies everything to the drive.

Now apple has this Time Machine software. Does this do away with the need to use Raid 1?

Assuming that i have 2 hard drives installed in my new MacPro. Do i want my second hard drive to be a Time Machine or a Raid 1 Copy? Pros Cons? What do you think?

[peeb]

What, you mean aside from the fact that they do completely different things?
RAID 1 does not protect you from accidentally deleting a file. TM does.

[mduell]

RAID1 (or any other mirroring scheme) and Time Machine (or any other backup scheme) serve two different purposes.

RAID1 is for availability; for servers that need uptime, the system (and possibly the data) will be run off of a mirrored array so that losing N-1 disks still leaves the server running. When you delete a file from a mirrored array, it's gone from all disks in that array.

Backups are for file recovery; they will often contain the same file at multiple points in time (generations). They protect you from your primary drive failing, applications or the OS corrupting files, etc; with an offsite backup they even protect you from fire/flood/etc.

You could use a RAID1 array as your Time Machine 'disk' if you needed higher availability for your backup storage.

[Reggie Fowler]

oh, i see.

lets suppose then that i want 2 hard drives in my computer. and i'll have time machine on the 2nd one.
does the time machine hard drive have to be the same size at the original. since it's storing multiple versions of the same file, i can only assume that the time machine hard drive has to be much much bigger. in fact, it seems that your time machine hard drive has to almost be unlimited because if it runs out of space, it will over-write the oldest point in time, therefore, defeating the purpose of time machine.

[SierraDragon]

Originally Posted by Reggie Fowler 

Assuming that i have 2 hard drives installed in my new MacPro. Do i want my second hard drive to be a Time Machine or a Raid 1 Copy? Pros Cons? What do you think?

Note Mark used the term "array" meaning a set of disks, usually identical disks. In fact RAID is an acronym for Redundant Arrays of Inexpensive Disks. All RAID configurations use/require multiple disks to achieve various different goals. Similarly, all RAID configurations have costs/consequences to use. In general righteous RAID arrays will always involve more than two disks total.

RAID 1 is perhaps the simplest RAID configuration, with the intent to maintain real time instant drive failure-proofing for enterprise-critical operations. There is a small performance penalty and decrease of total data storage space to configure two or more disks as RAID 1. RAID 1 protects against loss of data due to failure of a single hard drive. It does not back up data against fire, theft, software anomalies or operator error.

"Assuming that i have 2 hard drives installed" IMO unless one absolutely needs real time instant drive failure-proofing for enterprise-critical operations RAID configuration is a bad idea. Far better IMO is to use the second drive for Time Machine and/or Retrospect and other usages. Anyone who has instant-backup enterprise-critical needs should have more than two hard drives.

Generally folks considering RAID should be planning on more than two disks total. If one is thinking in 2-disk-total terms RAID is invariably inappropriate.

Note too that none of the above protect against fire or theft. Off site backup is also a necessity.

-Allen Wicks

[Reggie Fowler]

Why does using Raid 0 work faster than just using 1 hard drive.
Logically, i would think that copying or transferring files to 1 hard drive would be faster than spreading the data across two drives using Raid 0.

Does anyone know the transfer rate for comparison.
I see on the Apple website that Raid 0 can read at 304 mb/s and write at 245 mb/s

what are the read and write stats if you are just using 1 hard drive?

[peeb]

Wikipedia has a great article that explains all of this.

[mduell]

Originally Posted by Reggie Fowler 

oh, i see.

lets suppose then that i want 2 hard drives in my computer. and i'll have time machine on the 2nd one.
does the time machine hard drive have to be the same size at the original. since it's storing multiple versions of the same file, i can only assume that the time machine hard drive has to be much much bigger. in fact, it seems that your time machine hard drive has to almost be unlimited because if it runs out of space, it will over-write the oldest point in time, therefore, defeating the purpose of time machine.

The Time Machine drive can be any size as long as it's bigger than your data. It will of course eventually have to overwrite the oldest data, but it will keep at least one version of every file so you can restore it.

Originally Posted by Reggie Fowler 

Why does using Raid 0 work faster than just using 1 hard drive.
Logically, i would think that copying or transferring files to 1 hard drive would be faster than spreading the data across two drives using Raid 0.

Does anyone know the transfer rate for comparison.
I see on the Apple website that Raid 0 can read at 304 mb/s and write at 245 mb/s

what are the read and write stats if you are just using 1 hard drive?

With RAID0 (striping), you've put half of the data on each drive, so when you go to read it back you get half from one drive and half from the other, yielding twice the performance of one drive.

A single drive tops out at 80-100MBps; two drives in RAID0 would give you 150-190MBps (almost double but not quite), three would give you 200-250MBps (almost triple but not quite), four would give you 250-350MBps, etc.

[Reggie Fowler]

i'm still not understanding this Time Machine storage thing.

if my machine has a 100gig drive and 80 gigs is filled right now........that would mean the time machine drive would also be 80 gigs full? or does it not save version of the OS itself and all of the other system files?

and assuming the above to be true, lets say it's making backups every day. i think it would be just a few months before the remaining 20 gigs get filled.

does anyone have it setup. how big are your hard drives and your time machine drives? how much space are you using/available?

[mduell]

Originally Posted by Reggie Fowler 

if my machine has a 100gig drive and 80 gigs is filled right now........that would mean the time machine drive would also be 80 gigs full? or does it not save version of the OS itself and all of the other system files?

Yes, your Time Machine drive would also be 80GB full. It saves the OS files by default, but you could disable that if you didn't want it.

Originally Posted by Reggie Fowler 

and assuming the above to be true, lets say it's making backups every day. i think it would be just a few months before the remaining 20 gigs get filled.

It makes hourly backups; it keeps all the hours for a day, then it only keeps one backup from the end of each day for a week, and backup from every week before that. If your Time Machine drive was only 100GB then yes that remaining 20GB would probably get filled in a few months. Time Machine would then start deleting the oldest copies of files to make room for the newer files. Or you could buy a 500GB drive and use that for years of backups.

Originally Posted by Reggie Fowler 

does anyone have it setup. how big are your hard drives and your time machine drives? how much space are you using/available?

My parents have a 250GB drive in their iMac with 75GB used and a 320GB Time Machine drive.

[OreoCookie]

I definitely recommend to use Time Machine and not RAID1. The latter only improves reliability (in case of harddrive failure, your system doesn't stop working) and does not offer you the same safety a backup does.

[flabasha]

By the way, RAID 0 is much more dangerous than just a regularly formatted drive. It's advantage is raw speed (i.e. for intense video applications), but the downside is that the drive tends to corrupt very easily, and lose all the data.

If you're just backing up your drive with Time Machine, simply buy a 500gb external, plug n' play. That's all.

Only real reason to RAID drives is if you're cutting uncompressed HD or doing some other task requiring huge, fast, data throughput. And if so, use RAID 5 ideally. It creates the best data redundancy/performance profile, so it's still fast, but if one drive goes down, you don't lose everything.

[Reggie Fowler]

Ahhhh, i see. I see.

LAST QUESTION I PROMISE.

Does it matter if i get two 500 gig internal drives or do i want time machine to operate from an external 500 gig drive? Seems like it might be easier to have it as an internal drive??? Not sure if it matters.

And if the computer does completely crash and hard drive # 1 is corrupt, (and assume i have all my system software backed up via time machine on hard drive # 2)....once i format drive #1....how does copying work from the Time Machine drive in its entirety, back to drive #1, so that it would be as if nothing happened? A full restore i suppose. Is there an option to do so?

[OreoCookie]

In principle, both work, but it's much easier to deal with an external drive -- well worth the extra cost, and backups aren't really sensitive to the speed of the drives (as long as the backup has time to complete).

[SierraDragon]

Like Peeb recommended, anyone wondering about RAID should fully digest the Wiki white paper: RAID - Wikipedia, the free encyclopedia.

RAID solutions are no longer just for the highest end fringe of MP users. Today's MPs are very competent computers and the new MPs will provide even more competent performance. For most demanding apps today data i/o is the limiting factor on MPs once RAM and GPU are adequate. And, data i/o will be even more limiting on new MPs. IMO wise users of such heavy apps will be looking to spend on RAID 0, RAID 0+1, and RAID 5 solutions.

E.g. IMO RAID 0 properly used is almost a given for anyone setting up a graphics setup today. Most MP graphics users who do not implement RAID solutions with a new MP are limited by their hard drives. 2 drives plus backup are the minimum necessary for RAID 0 and another 2 drives are necessary to achieve RAID 0+1. RAID 0+1 (real time redundancy) is a luxury that I may or may not implement with a new MP but either way 3+ drives are a minimum to even attempt to optimize i/o for the kind of performance that any new MP will provide. Apple's $1000 RAID card makes the RAID stable and fast; exactly how much improvement over cheaper solutions I do not know.

Note that going after the performance bottleneck of hard drive i/o using RAID 0 proportionally increases the likelihood of data-losing hard drive failure. E.g. a 2-drive RAID 0, while 2x as fast also is 2x as likely to fail, a 3-drive 3x as fast and 3x as likely to fail, etc. Hence RAID 0+1, RAID 5 and other additional-drive-requiring schemata follow as necessary evils once one starts freeing up data i/o bottlenecks using RAID 0.

There are many ways to implement RAID solutions. E.g. for my Macbook Pro I use an OWC Firewire 800 external RAID 0 drive OWC Mercury Elite-AL Pro FireWire 800 + FireWire 400 + USB 2.0 + eSATA 'Quad Interface' Solutions up to 1.0TB at OtherWorldComputing.com for Photoshop scratch and for external images storage; works great, a big improvement over single-drive MBP performance, easy and inexpensive. The risk of data loss is insignificant for a RAID 0 scratch disk (since only the unsaved changes of one file are at risk), and image files are backed up to removable media prior to being worked with.

RAID 1 and RAID 0+1 are also available as simple external solutions.

I do recommend that folks buying external drives to improve i/o throughput buy the top end that have combined eSATA/FW800/USB2 connectivity. That will ensure backward and sideways compatibility to all computers. eSATA for the future or MPs if needed, FW800 for laptops and older pro Macs (and, with an adapter, FW400 Macs) and USB2 to connect to PCs (never to Macs).

One can buy slowest, lowest end drives for backup-only usages but IMO the low end of anything to do with data is always a risk. Buyers of the low end must be 100% comfortable with the validity and consistency of both their backup protocols and implementation.

-Allen Wicks

[Reggie Fowler]

Why is it easier to use Time Machine with an external drive? i would think an internal drive is easier because you never have to turn it on or even see it.

[SierraDragon]

Originally Posted by Reggie Fowler 

Why is it easier to use Time Machine with an external drive? i would think an internal drive is easier because you never have to turn it on or even see it.

Correct, internal drives are easy and hard drive replacement in MPs is easy.

Externals do allow portability to other computers and add flexibility for vault and off site backup. E.g. in the past I routinely locked up (Mac SE) external hard drives at night, and when computers were stolen the business impact was zero. Also, during the East Bay Hills Fire it was a simple matter to grab the external drives and stick them in the Volvo along with with photos, 3 dogs, 2 cats and a rabbit (no computers). The fire missed by only half a mile; 22 souls and 2500 structures lost. I add that last to try to impress that stuff happens: backup hardware and protocols are very real needs.

-Allen Wicks

[mduell]

Originally Posted by flabasha 

Only real reason to RAID drives is if you're cutting uncompressed HD or doing some other task requiring huge, fast, data throughput. And if so, use RAID 5 ideally. It creates the best data redundancy/performance profile, so it's still fast, but if one drive goes down, you don't lose everything.

RAID5 is a nice balance of capacity and protection; it is not a good solution for performance unless your RAID controller costs as much as a small house. Even at the $1000 controller level, the performance of a RAID5 array is about the same as a single disk.

All of the popular RAID levels have their place in a workstation.
RAID0: Fast scratch drives
RAID1: System/apps drive, so you can keep working even if a disk fails and replace when convenient
RAID0+1/1+0: Work in progress, same reason as above
RAID5: Long term storage with protection (probably an external enclosure)

[Reggie Fowler]

again, how does the restore feature work on Time Machine if i need to do a complete fresh install of my computer?

[mduell]

Pop in the Leopard install DVD and one of the options is recover from Time Machine. It will then copy the latest version of each file back to your hard drive.