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So you want to run a RAID array...
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Steven S Offline
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Post: #11
RE: So you want to run a RAID array...
so, got a second seagate barracuda 1TB, and the resulting array is actually SLOWER. go figure.

i thought RAID 0 will always be theoretically double the performance of the slowest drive. if that's the case, why would it be SLOWER when i have two matching drives?

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07-29-2011 10:33 PM
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Defiant Offline
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Post: #12
RE: So you want to run a RAID array...
(07-29-2011 10:33 PM)Steven S Wrote:  so, got a second seagate barracuda 1TB, and the resulting array is actually SLOWER. go figure.

i thought RAID 0 will always be theoretically double the performance of the slowest drive. if that's the case, why would it be SLOWER when i have two matching drives?

RAID 0 won't double the speed. It will have a boost when using 2 matching drives just as SLI with matching cards won't double performance.

Second, that tells me that the WD Black drive was faster. When you do benchmarks is the array's speed now consistent?

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07-29-2011 10:40 PM
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Steven S Offline
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Post: #13
RE: So you want to run a RAID array...
it's actually LESS consistent now. notice the big drop in write performance at 4096 KB:

[Image: 1tbseagatehddraid0.png]

and of course, the universally lower read/write. this ultimately doesn't affect me very much, since i use deferred write with fancycache. just a little disappointing, considering that a mixed RAID0 is actually faster.

i did gain a pretty big jump in random 4K read/write when i added a second intel 320 120GB though.

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(This post was last modified: 07-29-2011 10:57 PM by Steven S.)
07-29-2011 10:55 PM
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Defiant Offline
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Post: #14
RE: So you want to run a RAID array...
Are you using fancycache somehow during this test?

When you test the array you need to directly run the benchmark on it with as little as possible running in the background.

I would also see about upgrading the firmware on those 2 drives to ensure they are the same version, do that at your own risk though.

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07-29-2011 11:03 PM
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Steven S Offline
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Post: #15
RE: So you want to run a RAID array...
the two hard drives were bought new (finally got a colleague who smartened up and purchased one on the spot to swap me), so firmware are the same. in fact, both of them came out of the same shipping box.

as for fancycache, it's disabled for this benchmark. otherwise we'll be seeing around 6000 MB/s instead of 230 MB/s.

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07-29-2011 11:05 PM
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Defiant Offline
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Post: #16
RE: So you want to run a RAID array...
Since the forums had their little "uh oh" recently and we lost a weeks worth of posts, I'll redo my enterprise EVA/SAN write up.

At work we recently set up a new device call an HP EVA (Enterprise Virtual Array) which is HP's fancy way of saying "advanced SAN (Storage Area Network)". A SAN is basically a very large NAS used in an enterprise environment and will typically use interfaces such as iSCSI or fibre channel instead of the usual Gigabit or Fast Ethernet. HP changes this by adding a "virtual" edge to the array and allowing you to have multiple RAID arrays across multiple disks. This allows for expansion by adding more "shelves" (shelves shown in picture below). The RAID arrays you can have are actually applied to the "volume" of drives based on size of array rather than directly to the drives, therefore you could technically have 2 RAID arrays existing on 1 disk.

Here is a picture of what it looks like from the front (You may notice these hard drives, all 72 of them, look awfully small, this is because we are using 600 GB SAS 15K RPM 2.5 inch drives. Most rack servers these days actually use 2.5 inch drives to save space in the rack!):

[Image: EVA1.jpg]

Notice there are 4 "shelves" full of drives and a controller at the bottom (this particular controller is actually 2 controllers in one).

Also from the back, so you can see all the cables. Notice there are 8 fibre optic cables (4 are behind some power cords), this is what attaches the array to a SAN switch. Each of these 8 cables can sustain 8 GB/s:

[Image: EVA2.jpg]

Here are the SAN switches. Notice the 8 fibre cables now connect to them (4 each). One or two fibres will then go from this switch to each server to allow access to the array.

[Image: EVA_SAN_SWITCH.jpg]

Fun HP Licensing Fact: When you buy a HP SAN switch in either 8, 16, or 24 port flavor you are actually always getting a 24 port switch. By default only 8 of the ports will work until you go into the config page and enter a license key to unlock an additional 8 or 16 ports. They do this to make manufacturing the switches and upgrading them in the work place easier. Why order another switch and wait for it to ship when you can simply buy a license and have the ports available immediately?

Now, you are probably thinking about how access to this sort of set up works, your first thought would be a network drive and thats not true. Actually when using fibre channel or iSCSI the space you are allotted by the array controller is available to you on a block level, meaning you can format it or do whatever to it you wish as if it was a locally connected SATA drive. After connecting your server to the switch via a fibre cable you will have a volume appear in disk management as if it was a brand new hard drive which must be initiated and formatted. The volume you get depends on the port on the switch you use (configured on the switch and controller). The beauty of this versus a network drive is the speed, you could technically run your operating system off this array. We will not be doing this, however several VMs (Virtual Machines) will reside (be stored) here but be run on different servers.

Note: I've mentioned iSCSI a few times. it is a different interface used for small SANs, which uses network cables in the place of fibre (this means 1 or 2 GB/s). It allows the same "appears as local drive" functionality. Connecting to iSCSI is easy as Windows and Windows Server have an iSCSI initiator built in. Go look at "administrative tools" on your computer right now (in Control Panel), you have it to!

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(This post was last modified: 08-09-2011 10:52 AM by Defiant.)
08-09-2011 09:42 AM
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David Offline
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Post: #17
RE: So you want to run a RAID array...
I want one for my room

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08-09-2011 09:50 AM
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Peter M Dodge Offline
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Post: #18
RE: So you want to run a RAID array...
Aww, it lost the little bit wherein it was revealed how we were kinda talking past each other about RAID Tongue

Ive always had a fascination with the enterprise level computing stuff. Some kids have their candy stores, but for me its datacenters. Its a marvel to think my company is built on two little webservers colocated amongst literally hundreds maybe even a thousand other servers.

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08-09-2011 09:53 AM
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Mystryman Offline
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Post: #19
RE: So you want to run a RAID array...
(08-09-2011 09:50 AM)David Wrote:  I want one for my room

More space to store remixes of your favourite song?

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08-09-2011 09:54 AM
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Defiant Offline
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Post: #20
RE: So you want to run a RAID array...
(08-09-2011 09:53 AM)Peter M Dodge Wrote:  Aww, it lost the little bit wherein it was revealed how we were kinda talking past each other about RAID Tongue

Indeed, good times.

(08-09-2011 09:53 AM)Peter M Dodge Wrote:  Its a marvel to think my company is built on two little webservers colocated amongst literally hundreds maybe even a thousand other servers.

Its very possible that the actual storage being used for those servers is on an HP EVA or maybe a Dell SAN or otherwise. Unless you have them co-located there and manage the hardware yourself.
(08-09-2011 09:50 AM)David Wrote:  I want one for my room

You wouldn't be able to sleep, its very loud. Put it in the living room, makes a great coffee table/conversation piece (if they can hear you).

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(This post was last modified: 08-09-2011 09:58 AM by Defiant.)
08-09-2011 09:56 AM
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