Making the leap to RAID after my latest HDD failure. Got a few questions.

[IsenMike]

My storage drive, a 750GB Seagate Barracuda 7200.11, bit the dust recently. While doing diagnostics I realized that my OS drive, a 500GB Barracuda 7200.10, is showing some worrisome SMART values, and should probably get replaced soon as well.

The inconvenience and expense of sending the storage drive out to a data recovery specialist has me ready to jump on board the RAID train. Redundancy = awesome. Got a couple of questions, though.

1) How important is it that the drives are all exactly the same model? The 7200.11 is still under warranty, so I'll be sending it in for a new one after it gets back from data recovery. The 7200.11 has been replaced by the newer 7200.12, though, and I'm not seeing any of the older 750GB drives on NewEgg. Do I need to hunt them down to build a RAID 5 array? Or can I use one 7200.11 and two 7200.12's? (I'd be using the on-board controller on my EVGA 680i mobo, if that matters)

2) I'm going to start from scratch for the OS drive array. Getting tired of waiting forever for my computer to boot and to load programs, so I'd really like to boost the performance, but I need to stay within a budget (SSDs are out of the question, I'm afraid). What sort of difference would one expect between two VelociRaptor 10000RPM drives on a RAID 1 array versus three 7200RPM drives on a RAID 5?

3) I'll be going from 2 HDDs in my case to 5 or 6. How much of an issue is heat likely to be?

EDIT: Yes, I understand that RAID isn't a backup solution. Getting a large external drive for backup as well. (See below)

 

[RebateMonger]

Redundancy = awesome.

Redundancy = semi-awesome. There are things that can take out multiple disks as well as cause data loss even from a redundant array.

The primary purpose of redundancy is uptime rather than data security. RAID arrays, particularly RAID 5 arrays, do fail for sometimes obscure reasons. Even if you have a redundant RAID array, it's always recommended that you keep backups. I use RAID 1 or RAID 10 at business clients because of uptime concerns. But we still make multiple backups to prevent data loss.

For this reason, you might consider just buying one or more large ("slow is OK" storage disks for making backups of important data. Combined with automated backup software, it's much tougher to lose significant data this way than with a RAID array. Particularly a RAID 5 array. Recovery of a mutli-disk failure of a RAID 5 array is a "big deal" and I've seen several of them, unfortunately. Most are caused by user carelessness: Not paying attention to the array health.

In answer to your other questions:
* A RAID 1 array performs about the same as a single disk in both read and write operations. A RAID 5 array peforms faster reads but slower writes.
* You can mix disks in RAID arrays. Array capacity will be limited by the smallest disk and performance will be limited by the slowest disk, but mixed-model disks will work.
* Any time you put a bunch of high-speed disks together in the same case, heat is a concern. Vibration can also be a concern with RAID arrays because their head movements are synchronized.

If you do end up with a redundant RAID array, be sure to thoroughly read the disk controller manual so you understand how it works and what to do if a disk fails. Many manuals are not clear on array repair steps and making the wrong choice can cause loss of an entire array. It's not so bad with RAID 1, since the files are reproduced intact on both disks. It much more worrisome in RAID 5, where fragments of each file are on multiple disks.

If you end up doing backups, be sure to test your backups periodically to ensure they are working as expected and are readable.

 

[bigi]

Get a good, or very good HARDWARE RAID card. Those are expensive, but you'll be able to use one in several builds. I use RAID6 on 3ware 9650 8 port card.
Besides, do backups of your data because RAID does not equal backups in case the whole thing goes bad, etc.

1. HDDs don't have to be exactly the same model. I'd match capacity, RPM and cache.
2. RAID 5 tends to have slower writes, but it very much depends on the controller.
3. Heat is one of the worst enemies of HDDs. Keep in under 34 Celsius. Heat shortens HDD lives considerably, especially when over manufacturer specified threshold.

 

[IsenMike]

Okay, so here's what I'm thinking now: Still going with the RAID 5 array for the storage drive, but rather than building an array for the OS drive, I'll just be getting a single high-performance drive and spending the saved money on throwing two relatively-inexpensive 1.5 TB drives into a dual-drive external enclosure to use for regular full back-ups.

New questions:

1) How difficult would it be to, sometime down-the-line, throw a 2nd or 3rd matching high-performance drive in and migrate my system drive to a RAID 1 or 5? If it's just a RAID 1 array, can I just hook it up and have it mirror the existing drive as-is? Presumably migrating to RAID 5 would be much more complex, right? (Make a disk image on the back-up and start the array from scratch?)

2) What's a reasonable backup method? Simple file copying for the storage drive, disk imaging for the system drive? Any software recommendations?

 

[klocwerk]

Skip the RAID.
Get a cheap NAS box and do backups to it over your LAN.

RAID definitely has it's place, this is not it in my opinion. You just need good, reliable backups.

 

[Zap]

IsenMike, RAID is not a backup. If you value your data, you need backups whether or not you do RAID.

If you do end up with a redundant RAID array, be sure to thoroughly read the disk controller manual so you understand how it works and what to do if a disk fails. Many manuals are not clear on array repair steps and making the wrong choice can cause loss of an entire array.

This is a very good point.

 

[IsenMike]

IsenMike, RAID is not a backup. If you value your data, you need backups whether or not you do RAID.

Understood! See my reply above, where I mention dropping some of my RAID plans in favor of a 3TB external back-up drive.

 

[Evadman]

1) How difficult would it be to, sometime down-the-line, throw a 2nd or 3rd matching high-performance drive in and migrate my system drive to a RAID 1 or 5? If it's just a RAID 1 array, can I just hook it up and have it mirror the existing drive as-is? Presumably migrating to RAID 5 would be much more complex, right? (Make a disk image on the back-up and start the array from scratch?)

That depends entirely on the controller. Most low end controllers (implemented in software instead of hardware, and some hardware controllers) do not have ORE (online RAID Expansion) or RLM (RAID level migration). That means in order to add/remove capacity, or to change RAID levels (like RAID 1 to RAID 5) you must copy the data off the disk to another location, rebuild the array, then copy the data back. ORE and RLM allow changing the level & size on the fly, while keeping redundancy while the process is ongoing.

2) What's a reasonable backup method? Simple file copying for the storage drive, disk imaging for the system drive? Any software recommendations?

There are a multitude of options. Personally, I use robocopy with the /MIR option most of the time. It can run as a job in the background, you can schedule it for whenever you want, and it is fast. I have used several different backup software solutions, and they all ended up with the same result as robocopy. By the way, I am moving data from 1 NAS to another for backups, not local drives.

I use Acronis to make images of OS drives.

I'll just be getting a single high-performance drive and spending the saved money on throwing two relatively-inexpensive 1.5 TB drives into a dual-drive external enclosure to use for regular full back-ups.

Be careful with those. I have 3 of them, and none of them support a JBOD that is > 2 TB. That means that if you put two 1.5 TB drives in, you will only end up with 2 TB of space. They all support 1.5 TB disks though, they just have to be 2 volumes that are 1.5 TB each. That can complicate backups somewhat, so keep that in mind.

HDDs don't have to be exactly the same model. I'd match capacity, RPM and cache.

Careful here too. Here is a gotcha that I learned when crossing manufacturers. They don't all match size perfectly. For example, I had a RAID 5 array of twelve 750GB seagate and maxtor drives. One failed, so I got a 750 WD to replace it. However, I couldn't add the WD to the array, as it wasn't actually 750 GB. It was 749.999. Seriously. That made it so the disk didn't have enough space to be added, so I was left with a useless drive.

To remedy this, I wiped the array, and made it smaller by the same number of GB as there were drives. So instead of making it 7*750GB=5250 GB, I made the array size 7*749=5243 GB. That way, there was 1 GB of space on each disk that was not utilized, and made it so I wouldn't have the same issue in the future.

By the way, I also used varying cashe sizes, since in an array, generally you don't want to use the disk cashe anyway to avoid corruption on power outages. I just used whatever disk was cheap at the time.

I have since bought a UPS (and matching drives), so I turned the disk cashe back on, but I haven't noticed any performance increase or decrease. Granted, I didn't use a measuring tool, just 'seat of my pants' performance.

Any time you put a bunch of high-speed disks together in the same case, heat is a concern. Vibration can also be a concern with RAID arrays because their head movements are synchronized.

That can be remedied too. Since the OP is talking about a desktop and not case with hot swap bays, mount half of the disks upside down. Then the disks are about 180 degrees out of phase, which will cancel out most of the vibration from disks and any latent rotation (disks are now counter rotating). There will still be some vibration, since the head doesn't actually move left-right exactly, it also moves slightly towards the SATA connector. It isn't possible to cancel that out unless the drive is mounted upside down, and with the connector towards the front of the case. Most cases don't have room for that orientation.