A hint at things to come (in JackRabbit performance)

Well, this is a machine going out to a customer later today. Numbers aren’t so bad. Will explain a little more in a moment.

root@pegasus-i:~# dd if=/dev/zero of=/local/data.file bs=8M count=1024
1024+0 records in
1024+0 records out
8589934592 bytes (8.6 GB) copied, 40.328 s, <strong>213</strong> MB/s

root@pegasus-i:~# dd if=/dev/zero of=/local/data.file bs=8M count=1024 oflag=direct
1024+0 records in
1024+0 records out
8589934592 bytes (8.6 GB) copied, 25.6982 s, <strong>334 </strong>MB/s

root@pegasus-i:~# dd if=/local/data.file of=/dev/null bs=8M
1024+0 records in
1024+0 records out
8589934592 bytes (8.6 GB) copied, 19.5273 s, <strong>440</strong> MB/s
root@pegasus-i:~# dd if=/local/data.file of=/dev/null bs=8M iflag=direct
1024+0 records in
1024+0 records out
8589934592 bytes (8.6 GB) copied, 19.971 s, <strong>430</strong> MB/s
root@pegasus-i:~# dd if=/local/data.file of=/dev/null bs=8M iflag=direct

The machine has 4 GB ram. One of the updated RAID cards.

Whats so interesting about this?

That is 5x 7200 RPM SATA II drives in a RAID5 with no hot spare (at their request). That means 4x single drive speed is what we are seeing. About 75 MB/s per drive on direct writes, 50 MB/s or so on buffered writes, and 100 MB/s or so on reads, direct or buffered.

Now imagine 24 drives. A naive view would be 23/4 or (24-1)/(5-1) assuming performance was linear (huge assumption, it likely isn’t). Best case would be 5.75x faster than the above numbers. If these numbers hold, we should be seeing ~1.2 GB/s buffered writes, 1.9 GB/s direct writes, and ~2.4 GB/s reads. All sustained, far outside cache.

But, as usual, we will get to test this. On the test track. If we get 50% of this, I would be happy, as it would be on par with what we see on the older RAIDs.

I should also mention that we have not yet begun to tune.

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