# How much faster is SATA/RAID 0 ?



## eoJeoJ (Dec 19, 2003)

Hi everyone, just wondering if its worth it to get SATA (7200) drives and configure them to RAID 0...is the performance really that significant? What are the downsides of RAID 0? Thanks in advance.


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## cnimbus (Mar 1, 2003)

This link might be helpful:

http://www.anandtech.com/storage/showdoc.aspx?i=2101

Two important factors in hard drive performance are rotational velocity (i.e. RPM) and the controller to which the drive is connected. Of these, rotational velocity is the most important. The same drives may perform differently depending the controller used. This includes the RAID controllers built into mothererboards or the motherboard chipsets, as well as plug-in cards. Here is a link that illustrates these differences for a few controllers:

http://www.anandtech.com/storage/showdoc.aspx?i=1491.

RAID 0 is the fastest RAID level, both for reads and writes. The downside to RAID 0 is that the loss of one drive in the RAID array causes the loss of the data on all of the drives in the array. RAID 0 arrays are thus somewhat more prone to failure than JBOD (i.e. conventional standalone drive) configurations.


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## crjdriver (Jan 2, 2001)

cnimbus said:


> RAID 0 arrays are thus somewhat more prone to failure than JBOD


Actually this is incorrect. When you configure jbod, you are making two or more disks appear as one drive to the system; ie a 10 gig, a 20, gig and a 40 gig drive would appear as a single 70 gig drive. The same problem that raid 0 has about data being split between drives would apply in this case.

What I think you are referring to is two or more drives connected to the raid controller as independent disks; no array created on the drives. Each drive with it's own drive letter. That is not jbod.

To answer the question as to whether or not you will see any performance increase, on my system I see quite a performance boost. You will not see "double" the speed, however a 30% increase in hd access is more in-line with what you will see.


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## cnimbus (Mar 1, 2003)

crjdriver said:


> Actually this is incorrect. When you configure jbod, you are making two or more disks appear as one drive to the system; ie a 10 gig, a 20, gig and a 40 gig drive would appear as a single 70 gig drive. The same problem that raid 0 has about data being split between drives would apply in this case.


No, it is correct. The chances of data loss in a RAID 0 array increases with the number of disks in the array. This is because a failure on any one hard drive will cause the loss of the data on all the drives. It's not like RAID 0 is terribly unsafe. The MTBF for most desktop hard drives is in the hundreds of thousands of hours. All RAID levels present the array to the computer as one or more 'virtual' drives (the space on the array can be divided up into multiple virtual drives), or sometimes only one depending on the RAID controller.

RAID 1 provides significantly more data protection than JBOD. Maybe that was the RAID level you were thinking of? Or perhaps RAID 0+1? Some RAID controllers can also concatenate (as opposed to striping) separate drives into one large virtual drive. This is a form of JBOD, however, not RAID 0. It does not yield any performance improvement.



> What I think you are referring to is two or more drives connected to the raid controller as independent disks; no array created on the drives. Each drive with it's own drive letter. That is not jbod.


That _is_ JBOD (Just a Bunch Of Disks). With JBOD, a failure on one drive causes loss of data on that drive only. The data on the other drives remains intact.



> To answer the question as to whether or not you will see any performance increase, on my system I see quite a performance boost. You will not see "double" the speed, however a 30% increase in hd access is more in-line with what you will see.


A 30 percent increase is quite good, especially on a controller embedded on a motherboard or on many IDE plugin cards.

The 100 percent speed increase often cited might be with a caching RAID controller. Some controllers have cache memory on them, which lies in the data path between the hard drives and the computer. Data reads and writes to and from the cache are very fast, but only up to the point at which the cache is filled. After that, the data I/O speed drops to that of a non-cached RAID setup.

There is also a mistaken notion that SATA drives are always faster than parallel ATA drives. In theory, it is, but in fact often is not. SATA has a burst transfer rate of 150 MB/sec, as compared to 133 MB/sec and 100 MB/sec for Ultra ATA 133 and Ultra ATA 100, respectively. Burst transfer rate is into or out of the cache on the hard drive itself. As is the case with RAID controllers, the transfer rate slows down considerably once the cache is filled. Data is then written to and read from the drive platters directly, known as the streaming data transfer rate. At least initially, the streaming transfer rate was about the same for SATA and parallel ATA drives. SATA drives also have a lot more operational overhead than their parallel ATA counterparts. That is why many benchmarks show SATA as being slower. This, along with the streaming transfer rates, should improve quite a bit in the not-too-distant future.


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## saikee (Jun 11, 2004)

Think someone has reported a 260Mb/s transfer by some sort of measurements against the theoretical maximum of 300Mb/s.

Using it myself, now dismantled as one needed as backup, the RAID 0 is fastest I have come across. SATA as a single is noticeably faster and quieter than ATA133 but that is common with many SCSI drives. 

Serial drives are software driven and so there must be operational overheads.

I think a SATA may not perform much than a ATA is true in a case of one huge chunk of data transfer in one pass. In Windows operations with repeated loading and unloading of smaller files SATA can come out better.


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## crjdriver (Jan 2, 2001)

cnimbus said:


> No, it is correct. The chances of data loss in a RAID 0 array increases with the number of disks in the array. This is because a failure on any one hard drive will cause the loss of the data on all the drives. It's not like RAID 0 is terribly unsafe. The MTBF for most desktop hard drives is in the hundreds of thousands of hours. All RAID levels present the array to the computer as one or more 'virtual' drives (the space on the array can be divided up into multiple virtual drives), or sometimes only one depending on the RAID controller.
> 
> RAID 1 provides significantly more data protection than JBOD. Maybe that was the RAID level you were thinking of? Or perhaps RAID 0+1? Some RAID controllers can also concatenate (as opposed to striping) separate drives into one large virtual drive. This is a form of JBOD, however, not RAID 0. It does not yield any performance improvement.
> 
> ...


JBOD IS spanning of more than one drive. JBOD requires you to create an array. What you are referring to is connecting one or more disks to the raid controller; this is NOT JBOD. See this link for an explanation of JBOD. When you store data on more than one drive then the possibility of loss of data is just as much as with a raid array.

Here is another link explaining what JBOD is. The name is misleading, it should be called spanning which is what you are doing. When you span data, the chance of failure increases with each disk you add to the array.


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## crjdriver (Jan 2, 2001)

What you are doing is confusing JBOD with just connecting two or more drives to the controller. With JBOD the system "sees" just one drive even though you have connected two or three or more in a JBOD array. The data is spanned over the disks in the JBOD array; leaving just as much chance for data loss due to a disk failure.

When you connect two or more drives to the raid controller and do not create any array, then they are independent disks each with it's own drive letter. Data is stored on which drive you select. 

In reality JBOD does no real good. It increases the chance of data loss without any increase in speed. The only real use I can see for using JBOD is if you have a number of small hd and you want to make some use of them. Any critical data should not be stored on a JBOD array without backing it up to some other media.


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## JohnWill (Oct 19, 2002)

> The MTBF for most desktop hard drives is in the hundreds of thousands of hours.


I hope you don't base your backup strategy on that figure.  I really doubt any hard disk currently in production meets that figure in reality. Calculated MTBF numbers normally have little basis in reality, and this seems especially true for inexpensive IDE disks.


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## cnimbus (Mar 1, 2003)

crjdriver said:


> JBOD IS spanning of more than one drive.


JBOD CAN involve the spanning of more than one drive, but this is not an absolute requirement. The confusion may come from the way some lower-end RAID card vendors implement JBOD. Some of these boards will automatically span attached drives when doing JBOD. To make things even worse, their documentation refers to JBOD as a RAID level (I know some of the Highpoint cards do this), but that is an incorrect use of the term.

Some RAID controllers allow the user to turn the RAID feature off, making the controller act like just another ATA channel. Some vendors call this 'JBOD mode', while others call it 'standalone' or 'Ultra ATA' mode, or something similar. They are all equivalent.



> JBOD requires you to create an array. What you are referring to is connecting one or more disks to the raid controller; this is NOT JBOD.


That is incorrect. For drives to be presented as JBOD, it is required that they NOT be in an array. JBOD does not even require a RAID controller at all. Connecting disks to the controller has nothing to do with the RAID level or JBOD configuration used. How can the disks be accessed if they are not connected?



> See this link for an explanation of JBOD. When you store data on more than one drive then the possibility of loss of data is just as much as with a raid array.
> 
> Here is another link explaining what JBOD is. The name is misleading, it should be called spanning which is what you are doing. When you span data, the chance of failure increases with each disk you add to the array.


Whoever wrote the definition in those links, which are simply copies of the same text on Searchstorage, seems to know precious little about RAID and JBOD. JBOD does not require spanning, and to call it a derogatory term is nothing short of ridiculous. 'JBOD' is a technical term, and is not complimentary or derogatory at all. The Webopedia definition is both more concise and accurate.

If you want some better RAID info, try looking at the AC&NC, Finite Systems or Infortrend websites. 3Ware's RAID Primer also describes the various RAID levels and JBOD.


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## cnimbus (Mar 1, 2003)

johnwill said:


> I hope you don't base your backup strategy on that figure.  I really doubt any hard disk currently in production meets that figure in reality. Calculated MTBF numbers normally have little basis in reality, and this seems especially true for inexpensive IDE disks.


I agree that the MTBF figures given by vendors are usually on the high side. Just think of it as the reliability equivalent of benchmarketing. Even greatly reduced MTBF figures would lead one to believe that drives will last many, many years. In reality, the practical service life limits this number even further. I guess you get what you pay for. One of the biggest causes of premature drive failure is shock received by careless handling after they leave the factory.

Data that isn't backed up will be lost sooner or later. It is amazing how many home users don't do backups. This is especially true given that CD and DVD writers are relatively inexpensive.


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## saikee (Jun 11, 2004)

Never tried the feature myself but Linux as just an operating system claims to be able to span between two disks. I think if a problem develops one loses only the spanned system and the rest of the two hard disk should still be intact.

I agree backing up is essential if anybody wants to preserve his/her data. I find hard disks are superior as a backup medium. One can put any old drive into an external enclosure and hook up to the USB2 and enjoy a transfer rate faster than the CD-rw. There is no limit on the capacity also.

I use mobile racks and caddies on all my drives and have them fitted to external enclosures too. The drives can be used internally or externally at any one one time.


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## JohnWill (Oct 19, 2002)

I tend to use a variety of backup media, to better assure that I'll have the data when I need it. I backup daily to another machine on the network, and two-three times a day to my USB/Firewire disks. Finally, I store my really important source files and documentation on DVD-RW and store them off-site.


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