Netexpertise

You can open any kind of document on Windows from an AS400 5250 session or a CL.
The type of file can either be an image or a picture (jpeg, tiff, bmp, png), a video (avi, mpeg), a PDF, an office document (word, excel, powerpoint), and even an Internet link (URL).
 
AS400 provides the strpccmd command in this purpose:

strpccmd pccmd('explorer C:\répertoire\fichier')

 
The document will open with the default application as if when double clicking the file in explorer; Eg: Acrobat reader for PDF files.
 
Some say you don’t absolutely need the ‘explorer’ command to the document to open but it fixes some issues:
- You do not to get a DOS window displayed
- URLs launch with the default browser, Internet explorer or Firefox (This wouldn’t work otherwise)
- Documents with a space in the path aren’t buggy anymore

 

Tags: AS400

Based on advice from a Microsoft techie, I decided to set up DFS (Distributed File System) on a few remote sites about a year ago. Sceptical at first, The rpoduct is so disappointing that I decided to warn people who haven’t made their mind up.
 
Here are 6 good reasons NOT to use DFS:
 

No Defragmentation

After defragmenting, a new replication occurs generating a huge traffic that could max out your lines bandwith for a few days if the folders size is big enough.
I haven’t tried but I wonder if the same thing wouldn’t happen when creating/removing the disk index?
 

File Locking

There’s no such thing as inter-site file locking since there 2 local copies of each files (or more).
 

Concurrent Access

Drawback from the previous point, data may be overwritten. If someone leaves a file open the whole day and saves it before he leaves the office, all changes made from another replication site will be lost.
Therefore, DFS is advised for write-protected files or files that can be modified from a single site.
 

Failover

If one of the DFS server becomes unavailable on a same site, some users are still redirected to that server and may lose access to their files. Wasn’t it one of DFS goals?
Of course, users are still able to manually select the DFS target but most of them probably don’t know the trick. The problem does not happen on all folders as a DFS server is randomly selected for each one of them. There’s also a cache that defaults to 1800 seconds, that’s 30 minutes.
Solution: Upgrade to Windows Server Enterprise which provides clustering and rising the price of your license.
 

Diagnostic Tools

No graphical tool (yet Microsoft speciality) is available to monitor what’s being replicated.
There are indeed those scripts connstat.cmd and iologsum.cmd written in Perl (Really!?) provided with Microsoft support tools. You first need to relocate the files in a path with no space or you’ll get the following error:

Can't open perl script "C:\Program": No such file or directory

Microsoft have posted a bug report on their website back in 2007 rather than fixing it!
Try to replace “@perl %~dpn0.cmd %*” by “@perl %0 %*” around the end of the script…
Script usage is not very intuitive and information not always relevant in my opinion. Usage with a practical example is available on Microsoft indeed.
 

Bandwith Throttling

Bandwith throttling isn’t possible as far as I know on Windows 2003 Server…
As well as that, to stop an ongoing replication, I stop the DFS service. Nothing happens, replication still goes on. I had to run ‘net stop ntfrs’ to stop the flow. Unfortunately, this also denies Active Directory from replicating if you’re on a domain controller.
 
In a nutshell, DFS has so many gaps and restrictions, it becomes difficult to use it for anything but content publishing across an enterprise.

 

Tags: DFS, replication, Windows

Here are a few steps to configure iSCSI disks on Linux. Although I set this up on a Redhat Enterprise 5.5 connected to an HP MSA 2012i, the whole configuration remains generic and can be applied to any SAN.
I will add another post to check how both Linux and Windows perform on the same iSCSI device, since there has been a lot of issues reported on the net.
 

iSCSI Setup

First off, the iscsi tools package is required

# yum install iscsi-initiator-utils

 
Configure the security bit if any applied on the SAN

# vi /etc/iscsi/iscsid.conf
discovery.sendtargets.auth.username = My_ISCSI_USR_NAME
discovery.sendtargets.auth.password = MyPassword

 
I haven’t set any password the network being secured with vlans or dedicated switches. Authentication also adds up another layer of complexity while troubleshooting.
 
The hostname will appear on the SAN as configured on the server. Originially InitiatorName= iqn.1994-05.com.redhat:2ea02d8870eb, it can be changed to a friendly hostname for a simpler setup.
You can find it in /etc/iscsi/initiatorname.iscsi
 
Now you can start the iscsi service

# /etc/init.d/iscsi start

Make it persistent through reboots

# chkconfig iscsi on

 

 
Targets can be discovered with the iscsiadm command. I run it twice, once on each controller.

# iscsiadm -m discovery -t sendtargets -p 10.0.0.1
# iscsiadm -m discovery -t sendtargets -p 10.0.0.2

 
You can display them all

# iscsiadm -m node
10.1.0.1:3260,2 iqn.1986-03.com.hp:storage.msa2012i.0919d81b4b.a
10.0.0.1:3260,1 iqn.1986-03.com.hp:storage.msa2012i.0919d81b4b.a
10.1.0.2:3260,2 iqn.1986-03.com.hp:storage.msa2012i.0919d81b4b.b
10.0.0.2:3260,1 iqn.1986-03.com.hp:storage.msa2012i.0919d81b4b.b

 
Each new iscsi disk should be listed as /dev/sd[a-z]. Run “fdisk -l”. In a 2 controller SAN setup, each device is displayed as 2 separate disks. Read on the Multipath section to configure your device. If the SAN is equipped with a single controller, you can work with your /dev/sd[a-z] straight away.
 

Multipath

Install the multipath tools:

# yum install device-mapper-multipath

 
As advised on HP website, I set up /etc/multipath.conf as follow:

blacklist {
        devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
}
defaults {
        user_friendly_names yes
}
devices {
        device {
                vendor                 "HP"
                product                "MSA2[02]12fc|MSA2012i"
                getuid_callout         "/sbin/scsi_id -g -u -s /block/%n"
                hardware_handler       "0"
                path_selector          "round-robin 0"
                path_grouping_policy   multibus
                failback               immediate
                rr_weight              uniform
                no_path_retry          18
                rr_min_io              100
                path_checker           tur
        }
}

Leaving the device section commented out does not seem to actually apply, so this should work for any NAS as long as you make sure /dev/sd[a-z] devices are not blacklisted.
 
Turn multipath service on:

# modprobe dm-multipath
# /etc/init.d/multipathd start
# chkconfig multipathd on

 
Multipath device mapper will set disks with matching wwid (world wide id) together automatically. Display the multipath topology:

# multipath -ll
mpath1 (3600c0ff000d8239a6b082b4d01000000) dm-17 HP,MSA2012i
[size=9.3G][features=1 queue_if_no_path][hwhandler=0][rw]
\_ round-robin 0 [prio=2][active]
 \_ 8:0:0:30 sde 8:64  [active][ready]
 \_ 9:0:0:30 sdf 8:80  [active][ready]
mpath0 (3600c0ff000d8239a1846274d01000000) dm-15 HP,MSA2012i
[size=1.9G][features=1 queue_if_no_path][hwhandler=0][rw]
\_ round-robin 0 [prio=2][active]
 \_ 9:0:0:29 sdb 8:16  [active][ready]
 \_ 8:0:0:29 sdd 8:48  [active][ready]

 
If nothing shows up, run multipath -v3 for debug. Blacklisting is the most common issue on this.
 
Resulting partitions to work with are listed as /dev/mapper/mpath[0-9].
I initialize the disk with LVM for ease of use: I don’t need to go through fdisk after enlarging a volume on the SAN.

# pvcreate /dev/mapper/mpath0
# vgcreate myVolumeGroup /dev/mapper/mpath0
# lvcreate -n myVolume -L10G /dev/myVolumeGroup
# mke2fs -j /dev/myVolumeGroup/myVolume

 

LUN Operations

 

Add a new LUN

Once a new LUN has been created on the SAN, the server does not detect the disk until you do a refresh

# iscsiadm -m node --rescan

iSCSI disks are now visible, multipath automatically creates the new device.
 

LUN removal

After unmounting related filesystems, remove LUNs on the SAN and run “multipath -f mpath?” for the desired device
 

Expand volume

LVM is great as you can resize a physical volume instead of creating a new volume and adding it up in the volume group. Therefore, We stick with a clean configuration on the server and the SAN.
Refresh the disk size

# iscsiadm -m node --rescan

Check with fdisk -l disk size matches the size on SAN

# /etc/init.d/multipathd reload

Check with multipath -ll the device size has increased

# pvresize /dev/mapper/mpath0

The new disk space should now be available
 

Load-balancing and Failover

In this setup, traffic is load-balanced on the 2 NICs. If an interface goes down, all the traffic flows through the 2nd link.
I launched a big file copy on to the iscsi disk and turned off one of the interface. The CPU load goes high quick enough and drops as soon as the failover timeout has expired. The copy then fails over on to the 2nd link. Knowing this, set the timeout as small as possible eg 5 sec.

 

Tags: failover, HP, iSCSI, linux, load-balance, LVM, MSA, multipath, redhat, SAN, Storage