Raid 1 and Raid 10 vs Raid 5

[AlaskaFox]

Onboard vs Dedicated aside (understandably, Raid 5 requires more processing power for parity), I had a question/statement in regards to all the Raid recommendations I have seen here. Why is Raid either not recommended off the bat, or the recommendations that do come out for Raid 1 or Raid 10?

The way I see it is as follows. For a theoretical array of 4 500GB drives, the following statements should be true as I understand them.

Capacity
Raid 0 = 2TB (capacity = total of all drives, minimum 2)
Raid 1 = 2x 500GB (2:1 ratio, minimum 2 per set)
Raid 10 = 1TB (2:1 ratio, minimum 4)
Raid 5 = 1.5TB (capacity = total of all drives minus 1, minimum 3)

Redundancy (NOT BACK UP)
Raid 0 = NONE
Raid 1 = Single Drive Failure per mirrored set
Raid 10 = Single Drive Failure per mirrored set
Raid 5 = Single Drive Failure

Performance
Raid 0 = Fastest, performance increases with drive count
Raid 1 = Possible boost in speed for READ, no gain to possible loss (if noticeable) elsewhere
Raid 10 = Similar performance to its equivalent drive Raid 0 (ie 3 Drive Raid0=6 drive Raid 10)
Raid 5 = Between Raid 0 and single drive performance, goes up with drive count. processor intensive

With these statements, it seems to me that on a price vs capacity+performance comparison, Raid 5 comes out as the winner, the only fault being the extra processing power required (on software raid at least) for parity information on writes. otherwise, for the price of a single extra drive, one can have a similar level of fault tolerance, 66% of the available capacity (this also increases as drive count goes up, 75% available in a 4 drive array etc.) and descent read/write performance as compared to a 2 drive Raid 1 array with only 50% available capacity. This also allows gamers to have their boost in performance and have redundancy to boot. With more and more software based controllers offering this as an option, why not?

Disclaimer for those reading this to gain an idea of what array to go with, Raid for redundancy does NOT cover loss of data due to formatting, accidental deletion, viruses or any myriad of events leading to data loss. these do however offer protection against data faults and hardware failure (except Raid 0 with ZERO protection). having a Raid array is NO EXCUSE to not back up important data!

 

[UncleDave]

Onboard vs Dedicated aside - Why is Raid either not recommended off the bat, or the recommendations that do come out for Raid 1 or Raid 10?

As to why is RAID never recommended off the bat.... no idea. I think that having RAID 5 available on consumer motherboards is relatively recent. RAID 0 and 1 have been around for some time as such more people are familiar with them.

my 5c

p.s. Very well written

 

[einstein4pres]

Why is Raid either not recommended off the bat, or the recommendations that do come out for Raid 1 or Raid 10?

The way I see it is as follows. For a theoretical array of 4 500GB drives, the following statements should be true as I understand them.

Most people aren't planning on having 4 identical hard drives. Or even 3, the minimum required for RAID 5.

Also, it seems that most people seem to want RAID for either performance or for redundancy, not both. It's all a matter of priorities. If I were to buy multiple drives for an expensive system, I'd probably RAID 5 them (for simplicity, if nothing else). But I'm cheap.

 

[russki]

The vast majority of people seeking RAID on these boards are gamers that heard the RAID0 marketing hype and don't realize that in most desktop applications, games included, RAID0 has little to offer. Why people recommend RAID1 is funny, too, it's because most think of it as back up of sensitive data which it is really not.

Why anyone would recommend 10 is beyond me, unless you have $$$ up the wazoo to waste.

Why not RAID5? Well, that's because once you start thinking RAID5 you're getting to the applications that are not the scope of most inquiries. And you really need a decent controller to make it shine. And then, why not do 6 for better redundancy?

 

[The_Gremlin]

Redundancy (NOT BACK UP)
Raid 0 = NONE
Raid 1 = Single Drive Failure per mirrored set
Raid 10 = Single Drive Failure per mirrored set
Raid 5 = Single Drive Failure

I just wanted to clear up the slightly vague statement quoted (in bold), and also highlight the difference between RAID 0+1 and RAID 10 (RAID 0+1 not having been mentioned). They may perform identical and have the same capacity, but they are very different, and offer different redundancy.

RAID 0+1 (by far the more common)
Config - a mirror of two striped (RAID 0) sets.
Redundancy - UP TO TWO drives may fail without data loss, as long as the two drives that fail are part of the same stripe set (e.g. Drives 1 and 2 in pic-A below). If one stripe fails (one or both drives), it is still mirrored by the other striped set so no data is lost. If one drive from each stripe fails, then all data is lost.

RAID 10 (rarely suppported by onboard RAID controllers)
Config - a stripe set of two mirrored (RAID 1) sets.
Redundancy - UP TO TWO drives may fail without data loss, as long as the two drives that fail are part of different mirror sets (e.g. Drives 2 and 4 in pic-B below). So one drive of each mirror can fail without data loss, but if both drives of a mirror fail then all data is lost.

I don't remember where I read this, or the rational behind it (something based on statistics) but RAID 10 is considered to be superior to RAID 0+1.

Attempt at demonstrating the difference graphically:

PIC-A RAID 0+1 PIC-B RAID 10
______MIRROR______ ______STRIPE______
| | | |
_STRIPE_ _STRIPE_ _MIRROR_ _MIRROR_
| | | | | | | |
Drive1 Drive2 Drive3 Drive4 Drive1 Drive2 Drive3 Drive4

Hope this makes sense and helps add to the understanding of RAID!

 

[einstein4pres]

Why not RAID6? Because with the number of drives that most desktops will contain, the extra amount of backup (and increase in number of required drives) is not worth what you get out of it.

RAID6 is like RAID5, except you have an additional disk's worth of parity (aka backup) data, so if two drives die simultaneously (or while the array is rebuilding), you aren't fubared. The likelihood of this increases as the size of the array increases, so it makes sense with a sufficiency of drives, but for most consumer use, this is *way* beyond required.

As for RAID5, it provides some backup and some performance, without throwing away tons of capacity.

 

[russki]

Yet both are useless on the desktop. That's why by the time you start thinking RAID 5 you should be thinking RAID 5 or RAID 6.

In other words, I guess I am saying that if you're thinking RAID 5 you're really not a typical consumer, and then the increased cost is justified to improve redundancy. 'Cause the cost of downtime in most enterprise use is too high.

 

[RichKirk]

RAID5? This is the most abused RAID ever. No-one here has mentioned the really poor write speed of RAID5.

Because RAID5 has to calculate the parity bit, this makes it really poor for systems that write data. A web server is ideal as any input bypasses this and hits the 'back office' servers.

If you want reasonable performance use RAID1, if you need bigger capacity or 5x better performance, use RAID10
If you don't care for redundancy use RAID0 as this is the very fastest RAID.

I have tested and built hundreds of servers, mainly Database and Terminal Servers, but RAID5 has sucked on any occasion.

We once had an 8 disk RAID5 system which took 45 min to run a report, when replaced with RAID10 the same report took seconds!

PS And RAID6 is just another slow version of RAID5

Bottom Line: If you can afford 3 disks, then a fourth isn't going to kill you, otherwise stick with RAID1.

 

[gtvr]

RichKirk - the difference between RAID 10 and RAID 5 should not be as great as "seconds" vs 45 minutes. There was something else going on there. I have used RAID 5 in enterprise, database situations, and gotten good performance from it. Yes, RAID 10 is better, but not by multiple orders of magnitude.

There have been studies suggesting that due to soft error rates on HDs, RAID 5 is obsolete ( http://blogs.zdnet.com/storage/?p=162 ) although I think that is overstated. The point is, RAID doesn't replace backup, and it may or may not help your performance on the desktop much.

 

[Guest]

I am working in one of the datacenter in asia having top 10 largest SAN infrastructure.

In our latest enterprise SAN box, we're all configurate with Raid-5 group.

It gives reasonable performance in easy scalability in a storage infra. management perspective.

For SMB environment, i'd really suggest to go for Raid-10 but not Raid5, as the bottleneck is on the RAID controller processing CPU but not on the raid technology itself.

Also, the consideration on using either SATA or SAS disc for different raid type.

SAS disk can easily handle multi-spinning task. Therefore sometime even Raid-1 can do for most SMB application, however for the SATA disk(even enterprise grade) have to configure with higher IOPS raid group such as Raid-10 for better accessing time.

Of course if also depends on your budget, hope you guys could make a BALANCE choice.

 

[sminlal]

Redundancy (NOT BACK UP)
Raid 5 = Single Drive Failure

Performance
Raid 5 = Between Raid 0 and single drive performance, goes up with drive count. processor intensive

Both of these statements are either false or can be misleading.

In terms of performance, RAID-5 has very poor performance for writes. For each block of data you write to a RAID-5 set, the RAID subsystem needs to read the old data blocks AND the old parity blocks from the drives, recalculate the parity, and THEN write the new data blocks and updated parity blocks to the drives again. This makes RAID-5 unsuitable for many applications. And read performance is also much poorer in a degraded array.

In terms of reliability, RAID-5's ability to recover from a drive failure gets worse and worse the larger you make the array. This is because RAID-5 can only recover from a drive failure if it's able to successfully read EVERY block from EVERY OTHER drive. Most consumer hard drives are rated at up to one unrecoverable read error per every 10^14 bits read. That means that in an array of three 2TB drives you have as much as around a 60% chance of NOT being able to successfully read every block of data. RAID-6 is a much safer alternative since it can always recover unless you unrecoverable data blocks in the SAME PLACE on TWO drives - a very unlikely occurrence.

 

[KrazeyKami]

I see people here saying "RAID-5 has very poor performance for writes.".

Personally, i have a 260 MB/s write speed with 3x 2TB drives in RAID5, with an Onboard ICH10R controller. That's right, my RAID5 is writing faster then my SSD-X25M can read.
And in compare with RAID0 and RAID1:
RAID0 = twice the chance of losing all data (2-disk array; if 1 fails, all data is gone.)
RAID1 = only 50% storage capacity.

Personally i think RAID5 is the best solution on all grounds compared to RAID0 and RAID1, and the performance issue is heavily outdated.

My setup is almost Out-of-the-Box; no fancy tweaks.
The only thing that is important (and not to that much of a degree) is choosing the right Stripe Size vs NTFS Cluster Size.

In my case the most optimal was 128k Stripe and 32k NTFS cluster:

Seq. Read: 245 MB/s
Seq. Write: 261 MB/s

 

[andeljmp]

For database and high i/o demanding applications never use RAID 5 or 6
Because RAID 5 will do write actions twice, RAID 6 even 3 times.

Practical example:
ESX server with 4 * 500Gb Sata disks
max latency normal load
RAID 5 45ms (DELL standard config with performance issues)
RAID 10 2ms (after manual config to RAID 10)

Keep that in mind

 

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[casualbuilder]

So for internet and gaming, a RAID 10 would be the best setup? I would back up saved data on a USB as that is the only thing i would be upset if i lost, and the rest could be re-installed/re-downloaded. Am i correct in this thinking? I am running a mid-to-high-end gaming rig with a max of 4 HDD's installed.