another benchmark, more positive

howto/new-machine-cymru.md

@@ -1454,7 +1454,8 @@ general, you should expect:
  * iSCSI (network, large) disks:
    * read: IOPS=26.9k, BW=105MiB/s (110MB/s) (gigabit network
      saturation, probably cached by the SAN)
-   * write: IOPS=264, BW=1059KiB/s (1085kB/s)
+   * random write: IOPS=264, BW=1059KiB/s (1085kB/s)
+   * sequential write: 11MB/s (dd)
 
 In other words, local disks can't quite saturate network (far from it:
 they don't even saturate a 100mbps link). Network disks seem to be
@@ -1624,6 +1625,17 @@ load on the gnt-fsn cluster.
       sdj: ios=8678/8580, merge=0/0, ticks=6036/516604, in_queue=522552, util=99.77%
       sdh: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%
 
+### Raw DD test, iSCSI disks, chi-node-04
+
+`dd` fares much better, possibly because we're doing sequential writing:
+
+    root@chi-node-04:/var/log/ganeti/os# dd if=/dev/zero of=/dev/disk/by-id/dm-name-tb-builder-03-root status=progress
+    10735108608 bytes (11 GB, 10 GiB) copied, 911 s, 11.8 MB/s
+    dd: writing to '/dev/disk/by-id/dm-name-tb-builder-03-root': No space left on device
+    20971521+0 records in
+    20971520+0 records out
+    10737418240 bytes (11 GB, 10 GiB) copied, 914.376 s, 11.7 MB/s
+
 ### Comparison, NVMe disks, fsn-node-07
 
     root@fsn-node-07:~# fio --name=stressant --group_reporting <(sed /^filename=/d /usr/share/doc/fio/examples/basic-verify.fio; echo size=100m) --runtime=1m  --filename=test --size=100m