Help me choose the disks and raid type for a primary server. Raid 5 or 10?

[edutech4schools]

I am going to be switching out an old 2008r2 server for a nice new 2012r2 server at a small primary school.

 

I just read a DELL report saying they do not recommend RAID 5 or 50 anymore.

 

The old server has 5 250gb drives. 4 of the drives are in Raid 5 which gives a total of 700gb storage space, which is more than enough space. The 5th drive is a hot plug drive ready to kick in when one of the raid 5 drives goes down. This configuration gives us 2 drive failures before things are none recoverable.

 

I am currently building a replacement server and will probably be getting 1TB drives due to the good cost of these drives.

 

So do I get 5 1TB drives and config the RAID as the older server or do I look at alternative disk / RAID scenario, something like RAID 10.

 

Thanks for any advice.

[cscc]

RAID 5 + a hot spare sounds like a solid plan. If you also have a decent backup solution in place this would be sufficient. With something like RAID 10 you would end up losing roughly half the capacity.

[edutech4schools]

Thanks.

 

capacity probably is not an issue as they only use 400gb

 

So what would the usable capacity be of using 4 1tb disks in RAID 10. It's probably either 1 or 2 tb.

 

I have just been reading the following info and am getting a bit worried about Raid5

 

New RAID level recommendations from Dell - Spiceworks

[localzuk]

Anything in the TB range for HDDs, RAID 5 is basically a no-no now really. The chance of failure of the array during rebuild after a disk failure fast approaches 1 in 1. I did the numbers for this a while ago. If you really must use RAID 5, go to RAID 6 instead.

 

With RAID 5 - the chance of an unrecoverable error for a 7x2TB SATA array rebuild after a single disk failure is 62%.

 

RAID 6 tries to tackle this by allowing a rebuild to handle 2 such errors, by having more parity data. It does mean you lose an extra disk's worth of data in the array to parity data but its worth it IMO.

 

DO NOT use a hot spare. Really, really, really, bad idea. It removes the chance to ensure your backups have worked properly before kicking off a (potentially fatal to the data) array rebuild manually when you stick a cold spare in the machine.

 

However, ideally, people recommend RAID 10 ideally now. It also depends on the disk tech you're using, and its URE rate - SATA is mostly 10^14 or 10^15. SAS is usually 10^16. (ie. one error per 10^14 sectors etc...).

 

Personally, I'd look at using Windows Storage spaces and have the disks as JBOD now though to be honest! Its what I'm considering for the next server refresh here, that's for sure.

Edited January 22, 2015 by localzuk

[tmcd35]

I'm assuming you're using quality SATA drives like WD Reds? That being the case I don't think the cost difference between 1Tb and 2Tb is that great. You might be better served with 4x2Tb in RAID-10, it should be a little faster, than 4x1Tb in RAID-5 + hot spare. Also 4Tb vs 3Tb total capacity.

[edutech4schools]

The drives are SAS drives that come with a DELL T420 server.

[localzuk]

The drives are SAS drives that come with a DELL T420 server.

 

Real SAS or Near line SAS?

[Oaktech]

Interesting...

 

I'm not a million miles off having a NAS device and a similar choice to make - 8 bay qnap with 8x 2tb WD red disks in it (just because I can) capable of 0,1,5,10,JBOD.

[edutech4schools]

Real SAS or Near line SAS?

 

Lists it as Near line SAS.

[localzuk]

Lists it as Near line SAS.

 

Nearline SAS have SAS connectivity but are basically SATA disks, so higher chances of unrecoverable errors on rebuild in RAID 5.

[edutech4schools]

Personally, I'd look at using Windows Storage spaces and have the disks as JBOD now though to be honest!

Due to time constraints etc I will be sticking with RAID.

 

Nearline SAS have SAS connectivity but are basically SATA disks, so higher chances of unrecoverable errors on rebuild in RAID 5.

 

Taking in to account this is a primary school with limited funds would you,

 

1. Suggest getting a price for SAS drives? If so how many?

2. Stay with Nearline SAS drives but use RAID 10.

[localzuk]

I'd suggest using Nearline SAS but moving to RAID 10, rather than RAID 5. SAS adds quite a chunk to the price, as you can't actually get anything over 900GB SAS drives that I can see (I believe someone announced a larger drive recently but they don't appear to be commonplace), plus large size SAS drives cost a pretty penny.

[SHimmer45]

R5 if you understand the risks. its still a commonly used setup for reasonable storage sizes and offers decent performance / disk usage.

R10 is pretty much the go to Raid level these days.

another question to ask is if you have a failure how long can you be without access to the data, if something else breaks in the server or there is an issue with the array

 

i do like the look of mirrored arrays in storage spaces for the flexibility

[edutech4schools]

I'd suggest using Nearline SAS but moving to RAID 10, rather than RAID 5. SAS adds quite a chunk to the price, as you can't actually get anything over 900GB SAS drives that I can see (I believe someone announced a larger drive recently but they don't appear to be commonplace), plus large size SAS drives cost a pretty penny.

 

Thanks @lokalzuk

 

How many drives should I get? Does 5 1tb drives with 4 in RAID 10 and one standing by sound good?

[localzuk]

That'll give you a couple of TB of space, if that's enough then that'd work fine. I'd still keep the spare on a shelf rather than in the machine though.

[SHimmer45]

what hardware are you building the storage around?

[edutech4schools]

what hardware are you building the storage around?

 

This will be a DELL PowerEdge T420 with

 

Xeon E5-2430 2.2ghz chip

16gb ram

Raid controller not decided yet

5 years next day warranty

 

I have just contacted DELL to see how much a 'Real' SAS drive will be.

[DMcCoy]

This will be a DELL PowerEdge T420 with

 

Xeon E5-2430 2.2ghz chip

16gb ram

Raid controller not decided yet

5 years next day warranty

 

I have just contacted DELL to see how much a 'Real' SAS drive will be.

 

If you want to do more than RAID1 make sure you get the H710 (I think it is now) not the 200s which can be a bit slow.

[edutech4schools]

If you want to do more than RAID1 make sure you get the H710 (I think it is now) not the 200s which can be a bit slow.

 

Cheers for the heads up.

[edutech4schools]

Just had the following info back from DELL about RAID 5

 

I think what you’re referring to around the RAID is more geared towards SANs as opposed to servers. We never recommend RAID 5 in sans as detailed below (I believe the latest firmware actually prohibits using raid 5 is you try and change it to that yourself), however with servers RAID5 is still a perfectly viable option. Ideally RAID10 would be the preferred choice but that bring with it the additional cost.

 

Also had the quote back for 5 600gb 15K SAS drives and I think the school could be nudged in to paying the additional cost if preferred.

 

How much usable space would I get if I used them in R10?

[cscc]

About 1.2 Tb usable for 5 drives in RAID 10. Edited January 23, 2015 by cscc

[zag]

If storage space isnt a huge issue, you can get Intel 800GB SSD's for pretty cheap these days.

 

That will be more reliable than any RAID mechanical HDD setup in my opinion.

 

Something to consider anyway.

[DMcCoy]

If you have reasonable backup then RAID5 with only 5 600GB 15k SAS disks will be less of an issue. The 15k SAS drives usually have a BER of 100 times less than SATA disks, the chance of an error during a rebuild is very small. The *theoretical* chance of a rebuild being successful is at least 99.7% with SAS drives (with the same size SATA drives it would be only 78%, which is why you see the move from RAID5).

 

http://www.raid-failure.com/raid5-failure.aspx see what happens with big SATA disks!

[Oddbod]

Hmm, looks like I was right in choosing RAID10 ages ago, thanks for the raid-failure link!

[sparkeh]

Personally, I'd look at using Windows Storage spaces and have the disks as JBOD now though to be honest! Its what I'm considering for the next server refresh here, that's for sure.

Me too! I am in pretty much the exact situation as the OP and I'm probably going to use Windows Storage Spaces.

Good read about it (and some real world testing) here: Windows Storage Spaces and ReFS: Is it time to ditch RAID for good?

 

edit: quick note to say that ReFS currently doesn't support quotas which will be a deal breaker for some.