James Youngman's questions

Apologies if this is off-topic here (if so, is there a better place?).

I just bought a Unidata ICW-1000G WiFi phone (because I prefer to use just WiFi and not to use DECT). I'm attempting to do auto-provisioning with it by using the instructions in the Admin's manual. This proved more difficult than I had hoped as it's not written very clearly.

The basic idea for provisioning the phone is that by using DHCP option 66 we direct the phone to download a profile file from a provisioning server. My DHCP server is configured like this:

ddns-update-style none;
option domain-name "mydomain.org";
option domain-name-servers 192.168.15.19, 192.168.15.1;

subnet 192.168.15.0 netmask 255.255.255.0 {
  range 192.168.15.150 192.168.15.250;
  option routers 192.168.15.254;
  option broadcast-address 192.168.15.255;
}

host unidata-icw-1000-0 {
     hardware ethernet 00:03:2a:32:29:7b;
     fixed-address 192.168.15.35;
     option tftp-server-name "192.168.122.105";
}

The resulting DHCP responses look correct to me:

08:18:06.290021 IP (tos 0x0, ttl 64, id 0, offset 0, flags [none], proto UDP (17), length 315)
    0.0.0.0.bootpc > 255.255.255.255.bootps: [udp sum ok] BOOTP/DHCP, Request from 00:03:2a:32:29:7b (oui Unknown), length 287, xid 0xa94fcf3d, Flags [none] (0x0000)
      Client-Ethernet-Address 00:03:2a:32:29:7b (oui Unknown)
      Vendor-rfc1048 Extensions
        Magic Cookie 0x63825363
        DHCP-Message Option 53, length 1: Discover
        Client-ID Option 61, length 7: ether 00:03:2a:32:29:7b
        Requested-IP Option 50, length 4: unidata-icw-1000-0.mydomain.org
        MSZ Option 57, length 2: 576
        Parameter-Request Option 55, length 8: 
          Subnet-Mask, Default-Gateway, Domain-Name-Server, Hostname
          Domain-Name, BR, NTP, TFTP
        Vendor-Class Option 60, length 12: "udhcp 1.20.2"
08:18:06.290256 IP (tos 0x10, ttl 128, id 0, offset 0, flags [none], proto UDP (17), length 345)
    j.mydomain.org.bootps > unidata-icw-1000-0.mydomain.org.bootpc: [udp sum ok] BOOTP/DHCP, Reply, length 317, xid 0xa94fcf3d, Flags [none] (0x0000)
      Your-IP unidata-icw-1000-0.mydomain.org
      Client-Ethernet-Address 00:03:2a:32:29:7b (oui Unknown)
      Vendor-rfc1048 Extensions
        Magic Cookie 0x63825363
        DHCP-Message Option 53, length 1: Offer
        Server-ID Option 54, length 4: j.mydomain.org
        Lease-Time Option 51, length 4: 600
        Subnet-Mask Option 1, length 4: 255.255.255.0
        Default-Gateway Option 3, length 4: router1.mydomain.org
        Domain-Name-Server Option 6, length 8: ns-internal.mydomain.org,router0.mydomain.org
        Domain-Name Option 15, length 14: "mydomain.org"
        BR Option 28, length 4: 192.168.15.255
        TFTP Option 66, length 15: "192.168.122.105"
08:18:06.296638 IP (tos 0x0, ttl 64, id 0, offset 0, flags [none], proto UDP (17), length 321)
    0.0.0.0.bootpc > 255.255.255.255.bootps: [udp sum ok] BOOTP/DHCP, Request from 00:03:2a:32:29:7b (oui Unknown), length 293, xid 0xa94fcf3d, Flags [none] (0x0000)
      Client-Ethernet-Address 00:03:2a:32:29:7b (oui Unknown)
      Vendor-rfc1048 Extensions
        Magic Cookie 0x63825363
        DHCP-Message Option 53, length 1: Request
        Client-ID Option 61, length 7: ether 00:03:2a:32:29:7b
        Requested-IP Option 50, length 4: unidata-icw-1000-0.mydomain.org
        Server-ID Option 54, length 4: j.mydomain.org
        MSZ Option 57, length 2: 576
        Parameter-Request Option 55, length 8: 
          Subnet-Mask, Default-Gateway, Domain-Name-Server, Hostname
          Domain-Name, BR, NTP, TFTP
        Vendor-Class Option 60, length 12: "udhcp 1.20.2"

Here, the client is issuing a second DHCP query; not sure why, since it already got a respone.

However, the major symptom is that the boot server option doesn't seem to have any effect. The access log on the web server doesn't show the config file being fetched, and the error log also doesn't show a request for some other file (in, e.g. the wrong directory). The HTTP server works fine, I have a Digium phone on the same subnet which is provisioned using it. The HTTP server isn't used to serve anything other than phone provisioning files.

Using the admin console (via the phone's embedded HTTP server) I have been able to manually provoke the phone into fetching a configuration via the TFTP protocol instead but this isn't how I want to configure things as

1. It's not automatic anyway
2. I don't really want to use TFTP on my network at all

I understand from the Admin guide that I can use the TFTP server DHCP option to specify an HTTP server address as long as the "APS settings" in the phone specify HTTP as the protocol, which they do:

• Option = Setting
• Protocol = HTTP
• Use BOOTP 66 Option = Yes
• Use Provision = Yes

Any suggestions as to where I have gone wrong?

My question concerns only Linux software RAID ("md").

I'm going to set up a RAID1 array with three devices. I need to choose between using the third disk as a spare or as an active member of the array. There are no other arrays in the system, so there is no possibility of sharing the spare.

What's the performance impact of the third disk being routinely active? For example, what is the effect on tail latency?

If I go for three active devices, is there a data resilience advantage (e.g. can I scrub the array to take a three-way vote on the correct value of each byte? Apart from mitigating the risk of failure of a second device during reconstruction, is there any other reliability difference?