Subject: Re: RaidFrame poor performance
To: Greg Oster <>
From: Jochen Keil <>
List: current-users
Date: 01/20/2005 20:37:54
Greg Oster wrote:
> Jochen Keil writes:
>>At the moment i'm doing a benchmark on my 4 disk R5 setup and later i 
>>will do so on a 3 disk R5. What i'm wondering about is your comment 
>>about matching stripe size and file system block size.
>>Default FS block size is 16kb for partitions above 1024MB. I'm using 
>>this R5 Layout:
>>  START layout
>>            # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level
>>            32 1 1 5
>>I learned that 32 blocks equal to 16KB. As far as i can see my block 
>>size matches my stripe size so this is the optimum. 
> No.  In this case, with "4 data disks", a full stripe will hold 
> 4*32=128 blocks (64K) of data.  (That "32" is per-component.)
> So a block size of 64K will probably perform the best with this 
> configuration.

In case i misunderstood something: are you talking about four data disk 
plus one disk for parity which would sum up to five disks or do you mean 
four disks overall? To make my point more clear: wd0+wd1+wd2+wd3+wd4 or 
wd0+wd1+wd2+wd3? I meant wd0+wd1+wd2 for the three disk R5 setup and 
wd0+wd1+wd2+wd3 for the four disk R5 setup. I'm very sorry if this 
didn't came out very clear.
According to your and Daniels email a good R5 setup would be like that:
4 data disks + 1 parity + 1 hot spare. If i choose a stripe size of 32 
blocks the best FS block size i can choose would be 4*(32/2)K=64K.
Is this a correct conclusion?

If there is some interest i'll send my benchmark result to the list.

> Later...
> Greg Oster

Thank you very much in advance and with best regards,

Jochen Keil