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Raid and ssd performance questions

Posted on 2012-03-29
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Last Modified: 2012-06-27
Dear,
I want to buy new sotrage disks and I ask for your help:
1- Does Raid0 faster than Raid1?
2- Does Raid 2*SSDs is faster than 1 SSD?
3- My motherboard accept max of 3GB/S transfer rate, so do I will loose the performance of SSDs(6GB/S) and only works on 3GB/S ?
4- I am planning to buy 2 SSDs of 64GB for Operating System, and arrange them as RAID0, and make another RADI0 of 2 Normal HDDs of 3TB.
What do u think?
Thx
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Question by:hassanayoub85
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by:dlethe
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1) It depends.   In general, RAID0 is faster on all throughput, RAID1 is faster on IOPs. (I emphasize in general)
2) If properly configured, yes.
3) it depends on the motherboard architecture and the nature of the I/O
4) DONT DONT DONT.  Go RAID1.  Too much risk of data loss with RAID0, and unless you do nothing but run arbitrary benchmarks which IN NO WAY reflect how you will typically use a PC, then you will likely get better overall performance with RAID1 and Windows7 software RAID.
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by:hassanayoub85
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So do u mean it is better to go with:
- RAID1 2*128GB SSDs.
- RAID0 2*3TB HDDs.

my motherboard is intel dx58so.
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by:Sandy
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1- Does Raid0 faster than Raid1?
Yes Alwyas !!! Becuase Raid 0 Is STRIP and RAID 1 Is mirroring

2- Does Raid 2*SSDs is faster than 1 SSD?
No

3- My motherboard accept max of 3GB/S transfer rate, so do I will loose the performance of SSDs(6GB/S) and only works on 3GB/S ?

Yes !! It will

4- I am planning to buy 2 SSDs of 64GB for Operating System, and arrange them as RAID0, and make another RADI0 of 2 Normal HDDs of 3TB.
What do u think?

For OS i prefer RAID1, OK!!! but for data storage its perfect,

I have a suggestion here, you also can buy one more SSD and then go with RAID5
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by:hassanayoub85
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1- Why to go OS in RAID1? (I always do whole backup to an external storage, so if something wrong happened, I will recover. and in this way I will get the performace of RAID 0 instead of RAID1. Right?

2- What is RAID5? and does it's perfoormance same as RAID0 or RAID0 is faster?

3- in HDDs, Raid0 of 2 HDDs is faster than 1 HDD, so why in SSD it is not the same?

4- As I read, RAID 1 is just to make integrity between 2 SSDs, do if 1 fail other is active. Actually, I am not interested on this if it decrease the performance. Can u plz clarify more RAID1? and If RAID0 in SSDs don't increase the performance, so why to go RAID in SSD at all? as I am not interested in RAID1!!!??? Note: "dlethe" mentioned that RAID0 in SSD is faster, and u said it is the same. Plz clarify.
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For the most part, RAIDing SSDs is faster than a single SSD, but not in all cases.
These links are using Kingston, but should be similar to other SandForce based SSDs:

Conclusion:
http://www.xbitlabs.com/articles/storage/display/kigston-hyperx-ssd-raid0_7.html

Start of article:
http://www.xbitlabs.com/articles/storage/display/kigston-hyperx-ssd-raid0_3.html#sect0

start of benchmarks:
http://www.xbitlabs.com/articles/storage/display/kigston-hyperx-ssd-raid0_3.html#sect0
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RAID5 -- the short and dirty answer is it is a compromise between RAID0 and RAID1.
It gives you protection from a disk going out on you, and some performance increase, but not usually as much as a RAID0.
Plus you need at least 3 drives to set it up.
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by:dlethe
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I disagree.  One can configure any of the RAID0, 1, or 5 levels to be faster or slower then any other, if you are free to choose the type of I/O and configuration settings.

People tend to forget that there are two metrics, throughput and IOPs for every measurement of performance.  One is throwing money away if they buy SSDs for throughput.  SSDs aren't significantly faster then mechanical hard drives, so you can come out ahead if all you care about is throughput by purchasing a few extra mechanical drives to make up for it.  

A SSD makes sense for IOPS.   50,000+ random 4KB I/Os per second vs less then 100 for a mechanical drive.    Now if you look at throughput then figure 250MB/sec for this same SSD on writes vs 125 MB/sec on writes for a mechanical drive.

So in a RAID1 config I can get 100,000 random reads @ 500MB/sec  on SSD. In a mech disk figure 200 random IOPS @ 200MB.sec   (writes will be half)

Get an ECC error or have to go into recovery, and all I/O stops with a RAID0 while it recovers, if it can, or you end up losing data.  

But now consider that the SSDs are $500 and a mech HD with these numbers is $100.

If I wanted to get 1000MB/sec sustained throughput then I could do it with 8 disks for $1000. Or 2 SSDs for same amount of money.  But if I wanted 100,000 IOPs, then it would cost me $1000 for SSD but $500,000 in mechanical disks (plus much more for enclosures and power).

So depending on the benchmark the same performance characteristics could cost $1K or half a million dollars+ for SSD vs HD.

Using same disks, a RAID5 on mechanical drives would roughly be the sum of all parameters for the drive x (Disks in RAIDSET - 1).  But on WRITES??? It could be 1/3rd  the speed or less depending on the controller and cache settings.  On writes, RAID5 has to touch two disks at a minimum, plus do several I/Os because it has to figure out the parity and deal with the raid5 write hole.

Bottom line, generalizations are being used. Real world is not like benchmarks.  In a windows environment you are doing a lot of small block random I/O and you are almost always IO bound, not throughput bound.
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by:hassanayoub85
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Ok, last thing, what about the Bad sectors problem, does it found in SSDs too?
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by:dlethe
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Unreadable sectors and ECC errors due to bit rot and such affect everything.   It would take a lot of my time to cover this in depth, but suffice to say that the RAID level and controller type and error-recovery settings differ and their behavior differs.

The traditional desktop class drive in RAID5 config could easily cause the entire system to lock up for 30-60 seconds PER bad block.  However, with RAID1 and enterprise class drives, then I doubt you would even know if  a disk had a bad block, unless you were running a throughput benchmark.

Ever see your PC seem to lock up and do nothing, but the mouse still worked?   You were most likely seeing one of these deep recoveries.   This is why servers use enterprise class drives, because the firmware is tuned to give up after about a second because the premise is that the data you need can be extrapolated from the XOR parity. Desktop drives just stop and try to get your data and retry and retry and retry .. because premise is that you don't have them mirrored and there is only one way to get your only copy of that wedding photo and that it probably isn't backed up.
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Thank you much.    : )
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