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RAID 5 / RAID 10 question

Posted on 2013-01-21
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Last Modified: 2013-01-24
Hello,

I am looking to purchase a few ESXi servers.  I'm wondering what raid level would be better.

RAID 5 or RAID 10.  

I'm thinking if I do RAID 5, have like 7 disks in the array and one hot spare.  With RAID 10, I'm a little confused with how many drives can fail and if it requires a hot spare.

Overall, I'm thinking maybe 3 host systems.  Maybe 10 guest servers total.  However, I'm concerned with virtualizing Exchange and SQL and a file server.  How performance may be in doing this.  Currently they are on there own physical hardware.  Though probably one on each of those host systems.

The company isn't super intense.  We have about 65-75 users total.  One major SQL database everyone accesses.

I'm just not to confident in server sizing...  Haven't had much experience picking the hardware.  Looking to know if I'm on the right track and such.

Thanks...
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Question by:mmicha
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dlethe earned 84 total points
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First, you have two types of failures that create data loss.  Unreadable blocks and catastrophic drive failures.  The more likely failure is unreadable block.  

So in order to be protected against any data loss, then you need to have enough parity/redundant data to handle either.

In RAID5, 100% of the blocks each have one block for redundancy.  Lose either a single disk or any block and you are protected.   RAID10 effectively allows 50% of the blocks to have dual-failure protection, and 50% of the blocks to have single-failure protection.

Personally, since RAID10 has so many more benefits when it comes to performance, then just go RAID10.
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by:RickEpnet
RickEpnet earned 84 total points
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Raid 10 is much faster and it is possible to have more than one disk go bad and you are still up and running.

Raid 5 is pretty clear cut you have one disk go bad you are still running two disk go you are dead.

With raid 10 it is not so clear cut. Raid 10 has multiple raid 1 in them. So if you have 2 disk go bad from diffident sets you can still run if you have 2 disk go bad in a single set you are toast.
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by:mmicha
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So would you still have a hot spare for raid 10 setup?  A single array of it per virtual host the right idea if you are using DAS storage?
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by:cgitek
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RAID 1+0 (10) is cheaper too!

Speed is dependant on the controller, but dlethe is correct that it (10) is faster because it doesnt have to manage parity.
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by:dlethe
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If you want best possible data integrity and reliability, then you are much better off going RAID6.  RAID6 offers DUAL parity protection 24x7x365 for 100% of the blocks.

Both RAID10 & RAID5 offer only SINGLE parity protection 24x7x365 for 100% of the blocks ... with or without a hot spare.

But no free lunch.  RAID6's cost is I/O performance.

Better RAID controllers offer battery backed up cache modules for RAID controllers, which do  minimize the I/O write performance penalty,  and buying SAS-2 disks make a big difference.

One could even just add a pair of SSDs in a RAID1 and use them for scratch table space and leave the RAID6 for everything else.  But it just comes down to what you need.  If downtime and integrity is #1 on your list, then RAID6 is the answer. Period.
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by:Mekhalleh
Mekhalleh earned 83 total points
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Hello,
Generally the RAID 1 is named mirror. He use two disks (the one is mirror of secondary). Is used generally for support of the OS partition.
Is represented as follow : If I write XY on the first disk, I write XY on the secondary disk too.

The RAID 0 is named "streeping". He writes to both drives as a result. Is not mirror, if only one disk crash all is lost. He offer best performance for the OS (access file). Generally used for an system easy to rebuild (case of ESXi for exemple).
Is represented as follow : If I write XY. I write X on the first disk and Y on the secondary disk.

The RAID 10 generaly an implementation of two previous.

The RAID5 generaly used for the data storage (ESXi Datastore in your case).

The best way is : Mirror for OS. and RAID 5 for datastore.

Microsoft Exchange 2010 and SQL server works fine on virtualized environment.
If you need best response time for the SQL server you can install this on the physical machine (maybe is not your case).

Kind regards.
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by:Andrew Hancock (VMware vExpert / EE MVE)
Andrew Hancock (VMware vExpert / EE MVE) earned 83 total points
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RAID 5 is no longer considered a suitable RAID solution by the majority of vendors today.

Use RAID 10 for greater performance, or RAID 6.
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by:Mekhalleh
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RAID 6 Marketing :) sure RAID 6 is best. But is not supported by all RAID adapters.
And don't forget the backup.
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by:RickEpnet
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To answer your question about the Hot Spare yes if fact Raid 10 only uses even numbers of disk so if you have 7 disk there is nothing to do with the 7th disk except make it a hot spare.
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by:RickEpnet
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Remember Raid 6 is going to cost you in performance. But it does give you better redundancy.  Nice write up here
http://www.techrepublic.com/blog/datacenter/raid-6-or-raid-1-0-which-should-you-choose/2689
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by:Gerald Connolly
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@cgitek - RAID10 is not the same as RAID 1+0,

RAID10 is generally accepted to mean Striped-Mirrorsets (although i noticed that Dell had it defined otherwise on their support website, hopefully they have fixed it now!),

But the 1+0 and 0+1 notations are ambiguous because over the years different companies have used both to mean striped-mirrors and also mirrored-stripes
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by:RickEpnet
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I agree raid 0+1 is not Raid 10 but pretty much everywhere I look raid 1+0 is call raid 10 can you  please show us where raid 1+0 is not raid 10?

http://en.wikipedia.org/wiki/Nested_RAID_levels
A RAID 1+0, sometimes called RAID 1&0 or RAID 10
http://en.wikipedia.org/wiki/RAID
RAID 1+0: (a.k.a. RAID 10)
http://www.acronis.eu/resource/tips-tricks/2005/whats-raid-10.html
RAID 10, sometimes identified (and more appropriately so) as RAID 1+0
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by:dlethe
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It is ambiguous. Take it from me, who has written a heck of a lot of RAID firmware and configurators, both for hardware and software-based implementations.   Marketeers screwed up this terminology long ago.

Heck, I know of some hardware RAID controllers that support a "RAID10" configuration that supports an odd number of disks.  So moral of the story is to read the product and programming manuals if you want to know what you have.
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by:Gerald Connolly
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Thanks David.

@RickEpnet - Well if somebody uses/used 0+1 as Striped-Mirrors, then conversely they must have used 1+0 as Mirrored-Stripes. In a previous life i worked for Digital who did this.

Then there is this from Dell http://support.dell.com/support/edocs/software/svradmin/5.1/en/omss_ug/html/strcnpts.html#1176768 which actually says "RAID 10 can be considered a mirror of stripes."

To my mind the use of the 0+1 & 1+0 notation should be deprecated and we should all fix on using RAID10 which is commonly agreed (except by Dell) to mean Striped-Mirrors.

PS i have logged this faux pas by Dell last week, but as you can see it still hasnt been corrected - maybe they think its the right definition!
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by:dlethe
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just say mirrored stripes or striped mirrors and anybody that is worth listening to from technical perspective will be on the same page as you.
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by:Gerald Connolly
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I agree, but that will be too much typing for most people!
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by:dlethe
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Not if you only have to type it once ;)
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by:RickEpnet
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This back and forth is fun but we need to help this person make an informed choice. Bottom line raid 5 is fair performance where what is generally considered raid 10 is much faster and can offer a little more redundancy and if you have that hot spare you should be good for most things.
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by:Andrew Hancock (VMware vExpert / EE MVE)
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but it does really depend on the workload.

RAID5 is probably going to be okay, RAID6 better redundancy.
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by:dlethe
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Neither RAID5 nor RAID10 provide redundancy in all single-disk failure scenarios.  All it takes is one unreadable block on any surviving disk in a RAID5 (or one unreadable block in 50% of the disks of a RAID10) and you have partial data loss which could be really bad it munges up a database file or a registry.

You are also exposed to 100% data loss on a degraded RAID5 while it rebuilds, which is the most stressful time for a HDD.  You are exposed to 100% data loss for half the blocks on a RAID10.

Only RAID6 has dual-parity.  So with that many disks it could very well take all weekend to rebuild a degraded RAID5.   If you want to sleep during that time, spend a few hundred more on another HDD and go RAID6, or forego the hot spare and use that to go RAID6. Then you are protected against 100% data loss should a drive crap out during the rebuild, or even just get a read error.

You have 75 users who will have nothing to do but get angry if you go RAID5 and lose the data.   ask the beancounters what 75 employees cost the company if the system is down for a few days and if upgrading to RAID6 is a wise investment.

Then at least, when/if this happens, you can point to the person who said their time wasn't worth a few hundred dollars.
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by:dlethe
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Why not go for a hybrid.  RAID6 for the "DATA".  Get a pair of small SAS drives that can handle high IOPs and random I/O, and mirror them.  Put the O/S on them, plus index files and  scratch table space.   Maybe even go with a pair of small SSDs.  Even an inexpensive pair can give you 20K random 4KB reads per second verses a few hundred on SATA RAID6 (which should be set to 64KB I/O size).

Best of both worlds.
If you go SSD then they don't need to worry about vibration so just find some place to mount them internally, like were the CD/DVD drive is and use the SATA ports.  Then use the O/S software RAID1.
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by:Andrew Hancock (VMware vExpert / EE MVE)
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waste of money ESXi OS on usb flash drive or SD card, the storage is only used to boot the OS. only 1GB is required, then it goes memory resident, with very few read or writes to OS storage.
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by:dlethe
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I was referring to the O/S on the VMs.  But let's face it, if you desire performance, then don't virtualize the storage. Buy external RAID subsystems or use a ZFS-based appliance.
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by:mmicha
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I just gave everyone points for the feedback and assistance!  Thanks.
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