On 6/9/05, Gregory Tod <[EMAIL PROTECTED]> wrote: > Kevin - thanks for your input. I'd love to hear how it goes. Disk > performance has been the only issue with the 1750/3.5 combo: > > time dd if=/dev/zero of=/tmp/test bs=1024k count=1000 > > takes 55 secs or so...
I just now did a fresh installation of 3.7 from CD onto a PE1750 with a single RAID-1 logical drive (64KB stripe). The AMI BIOS was set with both WRBACK and CACHED-IO enabled: # time dd if=/dev/zero of=/data/test bs=1024k count=1000 1000+0 records in 1000+0 records out 1048576000 bytes transferred in 15.996 secs (65551409 bytes/sec) 0.0u 2.7s 0:17.83 15.6% 0+0k 20+48061io 0pf+0w # exit If I change the logical drive settings to WRTHRU and DIRECT-IO, the same test is literally an order of magnitude slower: xlog# time dd if=/dev/zero of=/data/test2 bs=1024k count=1000 1000+0 records in 1000+0 records out 1048576000 bytes transferred in 152.221 secs (6888484 bytes/sec) 0.0u 2.9s 2:38.29 1.8% 0+0k 17+48068io 0pf+0w xlog# In write-through caching, the controller waits for the drives to complete the write before signalling the OS that the write is complete. This is safe, but slow. In write-back, the data transfer is considered to be "complete" as soon as the controller cache has received the data, even if nothing has been committed to disk. The Cached-IO setting should only make a difference for reads, not writes. Kevin Kadow
