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Software RAID vs. Hardware RAID? *** NEW UPDATE - PLOT THICKENS ***

Stealth

Senior member
I am planning to setup a rackmount database server. I will be running RedHat Linux 7.3, and my motherboard has 2 Ultra160 channels, as well as 64bit PCI slots. I have 3 15,000 RPM SCSI Ultra160 HDDs to be used for the setup.

I am thinking about the following, but don't know which one is better in performance:

Software RAID setup (on both Ultra160 channels on my motherboard)
-or-
Hardware RAID setup - 64-bit Mylex ExtremeRAID Ultra2 (in 64-bit PCI slot).

Note that the hardware setup uses an Ultra2 SCSI card, not Ultra160. Any ideas on which will outperform the other?

Thanks in advance.

Shoot...the plot thickens...turns out that my mobo with the 64-bit PCI slot just blew...now I'm left with a board with 32-bit PCI slots (it also has onboard IDE RAID)...how does performance of the Mylex 1100 SCSI RAID 64-bit in a 32-bit PCI (3x15,000 RPM Ultra160 HDDs) slot compare to IDE RAID (2x7200 RPM ATA100)?
 
The hardware RAID solution will have lower CPU utilization than the software solution. Also, which RAID are you planning to use? Since you have 3 drives I am assuming that you are planning on RAID 5. In that case the hardware solution will be better as the porcessor on the card will be taking care of the parity calculations. The only downside to the hardware solution you hav is the the maximum transfer rate will be limited to 80MB/s. This should not be problem since your network connection will most likely be the limiting factor.
 
well, if you count the formatting of the array and the stripe etc then all RAID is software in a way. But as far as controllers are concerned you want a Hardware controller from Adaptec, Promise etc
 
There is little change in your CPU usage for raid 0 and 1 if you're using software raid. If you choose to use raid 5 you're going to HAVE TO use dedicated hardware (or suffer much).

I don't think the Ultra2 is going to bottleneck you very much. It might clip your burst speed a bit but that's all. The bottleneck always comes down to platter density and spindle speed. You're using 64bit PCI slots so that won't bottleneck either.

Do the Ultra2 raid controller. Best bet methinks.
 
How much CPU utilization are we talking about? The database server will be used as the backend of my site, which will have some forum software running in the frontend (as of right now, there will be 3 frontend servers). I will be running dual 1.26 Ghz PIII Tualatin's (512KB L2 cache) with 1GB RAM for the db server. And yes, I'm planning to run RAID 5.

What method would you choose if you were in my boat? Which is more ideal for a database server?

Thanks!
 
From the Vantage guide:

System Drive Configuration

The number of drives you purchase and how you decide to configure them is dependant on your budget, the intensity of your transactions, desired performance and need for fault tolerance. Budget will determine the # and speed of the disks you can afford. Intensity of transactions will predict what disk capacity your will need. Desired performance and fault tolerance will point you in the direction of some sort of RAID solution.

The major components of a Vantage system are:

1) Operating system
2) Vantage application code
3) Progress database files (D1, D2, LG?)
4) Progress Before Image (BI) file

In an ideal system, every one of these items would have its own disk, with the database files being located on a RAID10 set and BI files being mirrored for maximum performance and integrity. Given fewer disks, combining them involves some trade offs in terms of performance and integrity. The initial recommendation would be to never locate the database or BI files on anything but fault tolerate drives. Your data is worth far, far more than the additional cost of the required drives. The first components that could be combined would be the operating system and the Vantage application code. The BI file should be the last component you combine with something else.

Also, consider having a spare drive or two on the system. You?ll often find you need them later. It will let you have a spare copy of the database for testing, give space for expansion during a version upgrade or have a ready formatted drive in case of disk failure.

The Database Before Image (BI) file

The purpose of the before image file is to guarantee database integrity. The BI file itself is perhaps the most I/O intensive component of the system. Consequently, in a busy environment, the BI file should be on its own disk allowing the disk read/write head to remain positioned over the BI file reducing seek time and improving performance. In a hardware rich environment, the BI file should also have its own controller. Be aware that the performance boost you can experience by locating the database before image (BI) file on its own dedicated drive will be reduced if any other file activity occurs on that same drive.

In a transaction rich environment, with lots of reads and writes to the database, the Progress Before Image (BI) log file in particular is a bad choice for RAID 5. Its? sequential nature and high transactional volume are adverse to a striped set and the inherent write penalty of the RAID 5 configuration. When using RAID 5, locate only the Progress database files (DB, D1, D2?) on the RAID 5 array. The parity type of overhead doesn?t require as much additional disk space for these much larger database files, while still giving protection against single drive failures. Avoid locating the database BI file on a RAID 5 array.

Vantage processes like Global Scheduling, MRP, and new version Schema Updates, that by their nature perform a large number of writes to disk, will run slower when the database files are located on a RAID5 array. How much slower will depend on factors such as RAID technology (controllers, disk drives) implemented and the size of your database files. If your goal is to maximize performance, RAID10 will out perform RAID5 in terms of writes and offer similar read performance. If maximum overall performance is your goal, select RAID10 for your drive configuration.


For DB, I'd stay away from software RAID, especially with ATA disks.

Cheers!
 
Is your Mylex HBA an 1100 by any chance?

That will far outperform your mobo U160 HBA.

RAID5 is the way to go since you have three disks. If you have room, a fourth disk is recommended to be used as a hot spare. Depending on your access patterns, write back cache may be better or worse. In any case, if you decide to use the write back cache, it's extremely important to make sure your HBA has a BBU in good condition.

Cheers!
 
Shoot...the plot thickens...turns out that my mobo with the 64-bit PCI slot just blew...now I'm left with a board with 32-bit PCI slots (it also has onboard IDE RAID)...how does performance of the Mylex 1100 SCSI RAID 64-bit in a 32-bit PCI (3x15,000 RPM Ultra160 HDDs) slot compare to IDE RAID (2x7200 RPM ATA100)?
 
Originally posted by: Stealth
Shoot...the plot thickens...turns out that my mobo with the 64-bit PCI slot just blew...now I'm left with a board with 32-bit PCI slots (it also has onboard IDE RAID)...how does performance of the Mylex 1100 SCSI RAID 64-bit in a 32-bit PCI (3x15,000 RPM Ultra160 HDDs) slot compare to IDE RAID (2x7200 RPM ATA100)?

3 SCSI drives can easily max out the PCI bandwidth (133 MB/s). My 2 7200RPM ATA100 drives (RAID 0) reach a peak transfer rate of around 80 MB/s.
 

With your update to this thread I'm still going to cast my vote for the scsi raid controller. I'm using ATA raid for personal use and it blows a single scsi drive away but make no mistake the architectural differences between SCSI and ATA are huge. Hell you can't even do simultaneous read/writes on ATA. With a 32 bit PCI slot you may saturate the bandwidth on that bus at times but if you think about it, that's better than NOT saturating your PCI bus. Use Raid 5 on that controller and be done with it. It should run well.
 
Heh, I don't really even see it as a choice. Go with the SCSI controller. For business and heavy duty computing I don't think there is any other option. Its gotten better over the years (abit at aleast) but if you go software with RAID 5 you will take a MASSIVE performance hit.
 
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