# Question about hard drives, RAID 1 and WHS



## Kung (Jan 19, 2004)

Ok, I've got an Acer Aspire easyStore H340; it came stock with a Western Digital W20EADS hard drive (2.0TB, 32MB cache, probably 5400RPM). I'd like to add another hard drive (it's got an extra 3 bays, for a total of 8TB of storage), so I can implement RAID 1, at least. (Not sure if WHS supports software RAID; if so, I'll need to buy a hardware RAID controller, I suppose.)

My question is this - is it a requirement to have the EXACT same specs? I can find hard drives $20 cheaper that have 64MB cache, and same specs otherwise; but not sure how that might affect the RAID. Any thoughts? I'm sure it'll be fine, but would like opinions.


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## Txrider (Jun 25, 2010)

Kung said:


> Ok, I've got an Acer Aspire easyStore H340; it came stock with a Western Digital W20EADS hard drive (2.0TB, 32MB cache, probably 5400RPM). I'd like to add another hard drive (it's got an extra 3 bays, for a total of 8TB of storage), so I can implement RAID 1, at least. (Not sure if WHS supports software RAID; if so, I'll need to buy a hardware RAID controller, I suppose.)
> 
> My question is this - is it a requirement to have the EXACT same specs? I can find hard drives $20 cheaper that have 64MB cache, and same specs otherwise; but not sure how that might affect the RAID. Any thoughts? I'm sure it'll be fine, but would like opinions.


Better to have matching drives, age wise as well as model wise.

Also going cheap isn't always wise. Most of the cheaper drives are not engineered to last, and are not engineered for RAID use. They have an internal error recovery mode that will make them drop out of RAID arrays due to time outs on response. The larger the drives, the more likely this issue will get you.

http://en.wikipedia.org/wiki/Time-Limited_Error_Recovery

If you want good drives, go the HD manufactures site and get the model numbers for their enterprise class drives. 

They are built to last, high MTBF (mean time between failure) which is always something to look at on the drive you buy, I certainly do. They also have the short error recovery times so as not time out the RAID controller and drop out of the RAID array.

They do cost a bit more, but last much longer..

The controller you have or may get may also be TLER aware and not time the drives out, you may want to look into that.

Cache size isn't going to make big difference, you'll just be limited in write times to the slower of the two I would think. The controller should not be aware of the drives internal cache.


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## Kung (Jan 19, 2004)

Actually, going cheaper gets me the same quality drive with a 64MB cache as opposed to a 32MB cache.

Right now, I'm kind of 'limited' to what I have in my server; it's not enterprise class, I'm sure, but by the same token, we're not talking totally critical stuff here. For now I'm not too worried about MTBF, because I just got the thing; and to replace them would cost me a few hundred bux. So my question was more along the lines of what you stated in your last sentence - for now I just want basic RAID 1 mirroring. I figure that once one or both of these go, THEN I'll replace them with enterprise-class hard drives.

This being said, I absolutely agree with the rest of what you said.


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## arabian knight (Dec 19, 2005)

That Western D. HD is a 7200 rpm one, most all drives now days are at 7200. And the highest in capacity are now going at 10,000 RPM's


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## Nevada (Sep 9, 2004)

I've done a number of RAID mirroring installations. I did a few using the Linux software RAID solution, as well as several card & mainboard mounted solutions (I hesitate to say "hardware" solution since some RAID chips are still technically software solutions).

The fact is that the hard drive requirements vary with the RAID solution. Some require identical drives, and some require that the target drive be at least as large as source drive.

I haven't had any personal experience with drives with different access times or cache capacity, but I suspect that contemporary hard drives are fast enough that it's not an issue. I would go ahead and get the less expensive drives.

Most of the installations I've done included a hard drive capacity upgrade. Typically an engineer or land surveyor realized that he couldn't afford a hard drive failure, so looked for RAID as the solution. The upgrade would go something like this:



Buy a pair of large matching hard drives.
Migrate the entire old hard drive to new primary drive.
Configure the RAID mirroring array.
Duplicate the primary drive to the target drive.
Most clients didn't see any performance change at all by writing to two duplicate hard drives at the same time.

Sorry I couldn't be more help. I suggest that you select your RAID solution first, then do what the manufacturer recommends.


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## Kung (Jan 19, 2004)

Nevada said:


> I've done a number of RAID mirroring installations. I did a few using the Linux software RAID solution, as well as several card & mainboard mounted solutions (I hesitate to say "hardware" solution since some RAID chips are still technically software solutions).
> 
> The fact is that the hard drive requirements vary with the RAID solution. Some require identical drives, and some require that the target drive be at least as large as source drive.


Good point - I know 'how to do it' where I work, but it's been a LOOONG time since I've done a home use RAID install/implementation.



> I haven't had any personal experience with drives with different access times or cache capacity, but I suspect that contemporary hard drives are fast enough that it's not an issue. I would go ahead and get the less expensive drives.


Funny thing is that the cheaper drive is FASTER and has TWICE the cache. :shrug:



> Most clients didn't see any performance change at all by writing to two duplicate hard drives at the same time.
> 
> Sorry I couldn't be more help. I suggest that you select your RAID solution first, then do what the manufacturer recommends.


That makes perfect sense, especially since I need to figure out if I need to (or even want to) implement a RAID in my home server; and then need to figure out whether software will work or if I need hardware.

Reason I ask is because WHS does come with a 'hard drive balancing' thing, which essentially 'mimics' RAID 1. Thing is, however, that while it's easy as heck to set up (slap a drive in, then tell it to 'balance') I've seen complaints of slowing things down. RAID 1 would be faster, but obviously trickier to set up.

Your statement makes sense, however; thanks for the advice.


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