On Thursday November 9 2006 4:22 am, Arie Reynaldi Z wrote:
Software RAID level 1 is slower than 1 harddisk? Not true. Writing and Reading speed is good. But, it's the most expensive solution in terms of money per MB. Software RAID level 5 is slower than 1 harddisk? Partly true. Writing performance is a bit slower since it must calculate the parity. Reading speed is good.
I googled and found this: http://www.catux.org/index.php?contingut=articles&num=101
It shows that using software RAID 1 is slower then others.. Can someone explain about this ? It used Bonnie++ just like Joachim said.
regards, Arie Reynaldi Zanahar
As usual with benchmarks its what they don't document that really matters. That attempt at documenting RAID performance is lacking in details that really matter to the performance reported. In one chart it shows RAID1 as taking twice as long to complete as a single drive. Tells me that its probably IDE and both drives are on the same channel/bus; /dev/hda and /dev/hdb. There isn't any mention of how these drives are configured either in hardware or software. Are they on the same bus on the same controller? Are they spread across multiple busses and multiple controllers? Are these drives the same manufacturer, model number and firmware version? How are the drives partitioned and are they all the same? Is the system /swap on any of the drives in the test? If the system drive with /swap and / is on a separate drive is that drive on a channel/bus that the test drives are on? If the RAID1 drives are on the same IDE channel then only 1 I/O operation happens at a time and is a bottleneck. Since RAID5 needs a minimum 3 drives then at least 1 drive will be on a different bus and 2 I/Os can happen almost at once but 2 drives will be on the same bus and only 1 I/O will happen at a time there. Known bottleneck that doubles the time you think an I/O should take to complete. With basic IDE make sure you do something like /dev/hda RAID1 to /dev/hdc. Don't even put a CD/DVD drive on either /dev/hdb or /dev/hdd. Get more IDE controllers for more devices. So, what hardware do you have to work with, what will the system be used for, is data protection more important than performance? Stan