# new RAID-array: drives from different brands recommended?

## meulie

Hi all,

I'm about to purchase some drives that will form a RAID-array. Now I have read in various places that it's a bad idea to get all drives from the same brand/model/batch.

Should I really go for something like 1 Seagate, 1 Hitachi, 1 Samsung & 1 Western Digital drive?

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## snIP3r

 *meulie wrote:*   

> Hi all,
> 
> I'm about to purchase some drives that will form a RAID-array. Now I have read in various places that it's a bad idea to get all drives from the same brand/model/batch.
> 
> Should I really go for something like 1 Seagate, 1 Hitachi, 1 Samsung & 1 Western Digital drive?

 

hi!

what kind of raid do you want to build? hardware raid, software raid? and what raid level? i dont know the hw or sw solution will act if you use drives with different overall sector count.

i think the smallest count will be used for all other drives. my recommendation is to use identical harddrives.

HTH

snIP3r

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## overkll

IIRC, it is recommended to use identical drives for RAID.

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## Cyker

No, the drives have to be THE SAME SIZE, but other than that it doesn't really matter.

They should be of comparable speeds, otherwise all the drives will get bottlenecked by the slowest drive, but apart from that it should be okay.

The reasoning behind the "Use different drives" thing is that multiple-drive failure will "Kill RAID dead!"  :Razz: 

So, if you get all the same drives in one go, and it turns out there's a fault with the batch, you might be screwed (Esp. w/RAID0 which is tricky to recover data from, and  RAID5, which is near-impossible to recover data from!).

By buying different drives, the chances of a mass-fault are supposedly less, but it's all down to chance really.

My personal take is that RAID stands for Redundant Array of Inexpensive Disks so Ijust buy the cheapest non-crap drives I can lay my hands on  :Razz:   (i.e. makes like WD, Seagate, Maxtor, Hitachi, and not makes like Excel and Fujitsu  :Razz: )

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## jcat

I often hear people talk about the possibility of drives from the same batch failing, and I can well believe the theory.  But, the chances of more than 1 of a bad batch failing after 1000s of hours run time due to a common fault, and within a windows of say 2 days, are pretty minimal, maybe a couple within a month is possible.  And in practice I've never seen this happen (I've sys-admined 100s of different servers).

Therefore, a long as you replace a drive quickly when it fails (within a day or 2), you can't go too far wrong.  If you want to be really safe, then keep a redundant spare in the array for quick recovery to full redundancy level, the replace the spare when you can.

I recommend Seagate, as it's the brand I've had least trouble with over the years.

Cheers,

jcat

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## eccerr0r

I'm currently using in my software RAID5:

1 seagate 120G with 8M cache

1 maxtor 120G with 8M cache

1 maxtor 120G with 2M cache

1 post-seagate/maxtor merger maxtor 120G with 8M cache

Performance is not way too bad.  The only thing to watch out for is to make sure the geometries match, or don't use the portions of the disk where they don't match.  I've found the true maxtor disks are slightly bigger than the seagate-affiliated disks, so I had to use lowest common denominator and use the smallest of the set to make the array.

Personally the disks just need to be close to the same speed as possible, one lagging drive will slow down the array.  I've found if I have one disk doing self tests, the whole array's performance tanks.

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## meulie

I am considering going for RAID10 (RAID5 would be nicer, but write hole issue has got me spooked a bit, unless a UPS can get me around that?) & using 4x Samsung SpinPoint F RAID drives (HE103UJ).

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## drescherjm

 *overkll wrote:*   

> IIRC, it is recommended to use identical drives for RAID.

 

I would agree with that. For performance reasons you want each drive to perform the same and the only way to achieve this is all drives must be from the same batch. Sure you can mix and match drives but that will not lead to optimal performance. With that said the difference between optimal performance and not will not be more than a few % points so if you want you can mix drives. I generally do not and I have over 100 drives in linux software raid (5 and 6) at the moment.

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## drescherjm

 *Quote:*   

> RAID5 would be nicer, but write hole issue has got me spooked a bit

 

Not sure what you mean by that. I would say there is little to worry about with corruption. If you are worrying about the array being destroyed in a power outage.  At least that is not what I see on my side. To make a long story short the cpu in my home computer is defective (yet still works) so a few times a day it has memory / bus errors (machine check exceptions) but most of these are correctable. Some are not causing a kernel panic at least 1 time per week (got to swap out that cpu with the good one that sits on the shelf..) anyways none of this has caused any problems with the raid 5 array I have on that machine. And this has been going on since last year.

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## jcat

Proper RAID controllers have battery backups for their write cache, that prevents any data being lost before it was committed to the drive in the event of a power failure.

However, if there is no battery backup for the write cache you can disable the write cache itself, but I guess that will lead to a slight performance hit.  It's the usual balancing act between cost, performance, redundancy etc..  ..the choice is yours  :Smile: 

Cheers,

jcat

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## drescherjm

 *Quote:*   

> write cache you can disable the write cache itself

 

In my experience this leads to a huge performance hit. However I only have hardware raid controllers on windows since linux software raid in my opinion as good as any hardware raid on modern computers.

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## meulie

 *drescherjm wrote:*   

>  *Quote:*   write cache you can disable the write cache itself 
> 
> In my experience this leads to a huge performance hit. 

 

Does anyone know of a site where these have been compared? The only pages I can find so far all refer to hardware RAID, and I am interested in the performance loss with software RAID...

Anyway... Based on this it seems to me that RAID5 in combination with a UPS that is able to shut down the server when it needs to should be good enough to get a decent system...   :Cool: 

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## drescherjm

 *Quote:*   

> Based on this it seems to me that RAID5 in combination with a UPS that is able to shut down the server when it needs to should be good enough to get a decent system... 

 

At work that keeps my around 15 TB of software raid 5 and 6 (and growing 750GB drives are $110 US now) up and running. I equip each and every server with its own UPS that is rated at least 3 times the total power draw of the server. This way the UPSs will stay up for 30 minutes to 1 hour before they will need to power down. The good thing is that only 1 time in the last 2 years the machines powered down outside of that they have all been up 24/7/356.

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## meulie

Don't you mean 24/7/365.25?   :Wink: 

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## jcat

No need for floating point maths here.  Lets just say "all year round"  :Mr. Green: 

Cheers,

jcat

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## drescherjm

 :Laughing:  Typing error.

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