Re: File system performance, hardware performance, ext3, 3ware RAID1, etc.

[Timothy Miller <miller@techsource.com>]

Willy Tarreau wrote:
> On Fri, Feb 13, 2004 at 02:19:59PM -0500, Timothy Miller wrote:
>  
> 
>>Assuming that the "buffered" speeds are being buffered by the OS, we'll 
>>ignore those.  I am therefore observing that the writes to a single 
>>drive are 3 to 4 times faster than they are through the RAID controller, 
>>even with the 3ware write cache ON.
>>
>>Does that make any sense?
> 
> 
> Well, it reminds me a disk I had problems with several years ago. It had
> a few defects in the FAT area, which were relocated at the end. Performance
> was terrible since the head had to move constantly. It took ages to install
> Win31 on it, so it finally was returned to the vendor. But in your case it
> seems a little bit different since you experience slow writes anywhere on
> the medium. Would it be possible that your controller does something like
> read-modify-write because of too big chunk size ?
> 

I'm getting 10-15 meg/sec even with the largest block sizes.  With dd, I 
  set the block size to 1 megabyte, so there's no chance that the block 
being written is too small or that the disk block is too big.

Also, it's a RAID1.