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l008com · Nov 18, 2010, 11:25 PM

I have a first gen Mac Pro. For the past 4 years, it's been running on a software striped raid made from two 320 GB drives. These drives have gotten really slow. The seek time is about one second, from from like one nanosecond. So I need to replace this main volume with something better. I also have a single 250 GB disk for windows, that drive will be untouched. So I'll have three sata bays available.

So my first plan was to get three SSDs and put them in a software raid. If I got three 200 GB models, that would give me a respectable 600 GB of total space. And raiding already super-fast drives would give me even more super fast IO.

But then I saw the price of 200 GB SSDs. Still way too expensive for me.

So then I thought about just getting three 500 GB WD Caviar Blacks, and putting them in a software stripped raid. Or maybe even three 320GB. I don't really need 1.5 TB in my desktop.

Are there any other creative and reasonably priced options out there I'm overlooking?

P · Nov 19, 2010, 06:05 AM

Putting multiple SSDs in RAID doesn't really help all that much. Have you considered one SSD for the most critical files and two regular HDs in RAID 0 for the rest?

Note that RAID0 does not improve seek time, only transfer bandwidth. It is theoretically impossible to improve seek time after the fact (although it can be hidden with a large cache). What you can do is buy bigger drives and format them to only partial capacity. That does improve seek time slightly, as the driver head does not have to move all over the disk. Sounds crazy, but it does work.

There are also two more options with speeds between HDD and SSD: Velociraptor and Momentus XT. The first is just a very fast HDD. The second is a Hybrid drive that can be very fast at certain workloads when its SSD cache is useful.

OreoCookie · Nov 19, 2010, 08:43 AM

I would just get a 1.5 or 2 TB drive and be done with it. Even if you don't use the space, your data will just reside on the fastest part of the harddrive -- which is a good thing. If you want to selectively speed some things up, you can put your OS and the apps on an SSD.

500 GB drives aren't worth it anymore, I'd just forgo them.

PS If the seek times are really in the range `seconds,' something may be physically wrong with your harddrives. Which means they should be replaced asap.

olePigeon · Nov 19, 2010, 10:36 AM

You could get a 15000 RPM Hitachi 300GB drive for $250, plus $175 for a SAS RAID card. RAID a couple of those HDDs together.

Doofy · Nov 19, 2010, 12:08 PM

Originally Posted by l008com

Are there any other creative and reasonably priced options out there I'm overlooking?

Nuke and pave.

indigoimac · Nov 19, 2010, 01:43 PM

Get an SSD for boot and a 2TB for storage -- optionally get 2 2TB (or 1TB, whatever) and RAID 1 them so they're redundant.

demani · Nov 19, 2010, 01:53 PM

Absolutely: a SSD is the way to go for perceived speed, even if your data is on a slower (than the SSD) drive.

for example, ~$210 for a 100GB SSD
plus $90 for a fast 1TB hard drive. You get speed and capacity. Spend another $100 and get a greenpower 2TB drive for Time Machine backups.

Striping is a recipe for disaster, and rarely gets you much actual advantage unless you are doing a lot of data transfer (which, with 320GB drives, you aren't). SSD make a much bigger difference.

Waragainstsleep · Nov 19, 2010, 02:07 PM

I haven't experimented with booting from a striped RAID in a couple of years when I tried it out on a Mirror Door G4 with a pair of 400GB IDE drives. I got a massive speed boost for doing that but the setup crapped out very soon. I don't think it lasted a week before I had to reinstall. I imagine you might get more success with SSDs as performance is likely to be more uniform and hopefully software RAID is better now than it was under PPC Leopard (It might even have been Tiger), but whenever a customer suggests this to me I always tell them to fork out for a hardware RAID card to prevent them having to reinstall every fortnight or so.

I don't see why you wouldn't get a speed boost by software striping across two SSDs though. Even if I wouldn't trust it for something mission critical.

l008com · Nov 19, 2010, 02:37 PM

Originally Posted by Waragainstsleep

I haven't experimented with booting from a striped RAID in a couple of years when I tried it out on a Mirror Door G4 with a pair of 400GB IDE drives. I got a massive speed boost for doing that but the setup crapped out very soon. I don't think it lasted a week before I had to reinstall. I imagine you might get more success with SSDs as performance is likely to be more uniform and hopefully software RAID is better now than it was under PPC Leopard (It might even have been Tiger), but whenever a customer suggests this to me I always tell them to fork out for a hardware RAID card to prevent them having to reinstall every fortnight or so.

I don't see why you wouldn't get a speed boost by software striping across two SSDs though. Even if I wouldn't trust it for something mission critical.

You must have had some bad luck then. I've been using software stripes for years and years, at least since a MDD myself, possibly even before that. The only problem I had was when 10.5 first came out, and it wasn't really fully compatible with SoftRAID. I ended up having to reformat as an appleraid. But you just restore from time machine and you're good. I don't know why people would say a stripe raid is dangerous at all. Just restore from a backup if anything ever goes wrong.

Also my seek time isn't literally 1 second. But it's getting very slow. My drives aren't "failing", but they are getting very old at this point.

I'm not a big fan of splitting up systems among different volumes, so I really don't like the idea of "some stuff on an SSD, some on an HDD".

Also for those that claim a stripe raid won't give you must of a speed boost, I suggest you try it out. x2 is a pretty good speed boost.

seanc · Nov 19, 2010, 05:04 PM

Stripe is dangerous if you don't keep backups.

Try Western Digital RE3 drives, they're OK, not the cheapest.

l008com · Nov 19, 2010, 05:06 PM

Yeah but who's not going to backup. Non-RAID is dangerous if you won't keep backups.

seanc · Nov 19, 2010, 05:14 PM

Plenty of people don't and it almost always comes back to bite them.
I had one this week. "Can I have my data?" "Sure, give me your backups." "What backups?" "Oh this was a striped RAID, definitely no data".

Yes, all situations where there are no backups are dangerous, however with single disk failure, I can usually keep it going long enough to get the data back. With striped I have to hope the software raid solution keeps working, or that the hardware raid device doesn't fail/get killed by a liquid cooling system.

Note, there is no value to my post, except to explain my views towards the scenario where you meet an end user, and there is not a current backup. I am aware that backups are a must, but not all home users do that, nor do they realise how their 640GB volume in their off the shelf PC works (2 x 320GB stripe).

P · Nov 19, 2010, 05:15 PM

While I don't see a reason to use RAID at all, the OP has been doing so for some time. RAID0 provides a noticable speed boost when it comes to transfer bandwidth, but zero advantage for access times (seek time). What do you really need - seek time or bandwidth? If it's bandwidth, then get the biggest drives you can afford (WD Black is a nice choice, but bigger than you suggest) and put them all in one big RAID0. If it's seek time, then it's either the SSD setup (which you don't like), a Velociraptor or partition tricks with a bigger drive.

l008com · Nov 19, 2010, 05:20 PM

Originally Posted by P

...I don't see a reason to use RAID at all . . . RAID0 provides a noticable speed boost when it comes to transfer bandwidth

Originally Posted by P

While I don't see a reason to use RAID at all, the OP has been doing so for some time. RAID0 provides a noticable speed boost when it comes to transfer bandwidth, but zero advantage for access times (seek time). What do you really need - seek time or bandwidth? If it's bandwidth, then get the biggest drives you can afford (WD Black is a nice choice, but bigger than you suggest) and put them all in one big RAID0. If it's seek time, then it's either the SSD setup (which you don't like), a Velociraptor or partition tricks with a bigger drive.

It's not that I don't like SSD, it's that I don't yet like it's price. When fast 200 GB SSD drives are $100, I'll be all over it. Is there an app to benchmark seek times? I want to compare the old drives in this machine to some much faster newer drives I have in other machines.

Also yeah at this point it looks like I'll just get two or three fast desktop HDDs and put them in a fast raid.

demani · Nov 21, 2010, 12:00 AM

Well, because the potential of failure is twice what it is if you don't stripe. And $100 will certainly get you a screaming fast boot drive (where your main random seek is occurring) and let you use a pretty fast drive for your files (which are rarely running through a lot of seek operations- or RAID those).

Are you doing a lot of large file transfers? That's where striping helps. But if you aren't, then it's not giving you a significant boost, and it isn't worth doing (those statements make perfect sense when considered together). Again, if a pair of 320GB drives is doing it for you then it's likely you aren't going through big files. And again, 320GB drives aren't even close to the performance of current model drives.

You can download Drive Genius to test your drive (I believe the demo will let you benchmark). See what your current set up actually is.

besson3c · Nov 21, 2010, 12:40 AM

The only thing I can think of would be to setup an OS with a better (faster) file system to use these disks and turn that machine into a NAS.

For instance, if you were to do this with a Solaris machine running ZFS you could setup a pool to include an buffer for reads or writes that utilizes an SSD, as well as dedicated RAM which ZFS will make full use of.

This is probably geekier than you'd want to go, but suffice to say I'm a major fan of ZFS based file servers for a whole plethora of reasons (snapshots being a big one!).

besson3c · Nov 21, 2010, 12:41 AM

Originally Posted by demani

Well, because the potential of failure is twice what it is if you don't stripe. And $100 will certainly get you a screaming fast boot drive (where your main random seek is occurring) and let you use a pretty fast drive for your files (which are rarely running through a lot of seek operations- or RAID those).

Are you doing a lot of large file transfers? That's where striping helps. But if you aren't, then it's not giving you a significant boost, and it isn't worth doing (those statements make perfect sense when considered together). Again, if a pair of 320GB drives is doing it for you then it's likely you aren't going through big files. And again, 320GB drives aren't even close to the performance of current model drives.

You can download Drive Genius to test your drive (I believe the demo will let you benchmark). See what your current set up actually is.

Good advice here about striping...

l008com · Nov 21, 2010, 04:42 AM

So I have to admit, I'm starting to come around on this dual-volume idea. Except that even that's more than I really want to spend. A 128 Gb SSD is about $235. Add a pair of 500 GB WD Blacks for a 'user' software raid, and I'm up to about $350. I could do just HDDs, and go with three 500 GBs for $180. And when I think about the other upgrades I want to do, 4 GB more RAM, and two new monitors... I dunno. Tough call.

P · Nov 21, 2010, 11:03 AM

What is it that you're after - transfer bandwidth or access times? You said access times, but then you keep wanting RAID, and RAID doesn't improve access times at all. If it is access time, then buy one SSD and use the existing drives in a RAID or JBOD - except reformatted and reinstalled. If it's bandwidth, then don't bother with the SSD.

OreoCookie · Nov 21, 2010, 02:34 PM

Also, you keep on going back to 500 GB drives: they will be slow compared to up-to-date 1.5 or 2 TB drives. Not only does the data reside on faster portions of the drive, the platters in all likelihood have a larger data density which improves throughput significantly. Exact numbers depend on the specific hard drives you're interested in, but it could very well be that a fast 1.5 TB drive is not much slower than a RAID0 of two slower 500 GB drives. And you'd save money.

l008com · Nov 22, 2010, 03:08 AM

Originally Posted by P

What is it that you're after - transfer bandwidth or access times?

Yes

l008com · Nov 22, 2010, 03:13 AM

Here's something that's been nagging me. It's been said that a stripe raid won't effect seek times. But it should. I have the same amount of data, whether I'm using a single drive or a pair of stripped drives. So if I'm using a strip, each drive has half the amount of data, and so that data should be stored on faster parts of the drive, and it should be physically closer together than if it was all written on a single drive. It wouldn't be a huge boost, but there should be some boost there.

OreoCookie · Nov 22, 2010, 04:03 AM

Originally Posted by l008com

It's been said that a stripe raid won't effect seek times. But it should.

Striping does have a slight negative effect on seek times: the computer has to wait until both drives have found the relevant location on the platters. That is independent of whether the data is located on the `fast' or the `slow' part of the drive. When you say fast or slow part of the drive, you refer to throughput, not seek times.

Originally Posted by l008com

I have the same amount of data, whether I'm using a single drive or a pair of stripped drives. So if I'm using a strip, each drive has half the amount of data, and so that data should be stored on faster parts of the drive, and it should be physically closer together than if it was all written on a single drive. It wouldn't be a huge boost, but there should be some boost there.

No, seek times would be slightly slower than a single drive. If you compare the same drives, throughput of the striped drives will be faster. If you compare a fast large drive to an array of slow small drives, it's no longer clear. The data density of the platters of the large drive is typically a lot larger than that of the smaller 500 GB drives.

OreoCookie · Nov 22, 2010, 04:06 AM

Originally Posted by l008com

Yes

It was an either or question, not a yes/no question.

l008com · Nov 22, 2010, 04:08 AM

Answering an either/or question with a yes/no is the dickish way of saying 'both' or 'neither'.

OreoCookie · Nov 22, 2010, 06:21 AM

I know. But why do you even see the need to answer like that? We're trying to help.

besson3c · Nov 22, 2010, 09:40 AM

Originally Posted by l008com

Here's something that's been nagging me. It's been said that a stripe raid won't effect seek times. But it should. I have the same amount of data, whether I'm using a single drive or a pair of stripped drives. So if I'm using a strip, each drive has half the amount of data, and so that data should be stored on faster parts of the drive, and it should be physically closer together than if it was all written on a single drive. It wouldn't be a huge boost, but there should be some boost there.

This is incorrect. Even if you are talking about one giant file, all a stripe buys you is more I/O bandwidth to saturate, not faster seek times. Seek times are dependent on the slowest disk in the stripe.

P · Nov 22, 2010, 04:51 PM

Originally Posted by l008com

Answering an either/or question with a yes/no is the dickish way of saying 'both' or 'neither'.

OK, so you just want a fast HD, but you don't really have a use case for either situation.

Buy a Sandforce-based SSD - 128GB would probably be enough, but the bigger the better. Install your OS and commonly used apps on it. Backup and then wipe your existing drives, and then use them as your big data disk in a RAID0 setup. This will "feel" very fast and you can bring the SSD to your next Mac when you upgrade. That is what I suggest you put the rest of the money you might have - in a piggy bank towards the next upgrade.