CLI

Recovering a failed RaidZ pool

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Scenario: A drive is your RaidZ pool has gone bad. You have a replacement drive ready to go. You pull the drive you thought was the failed drive.. only to realize that you just pulled a good drive out, causing the array to go completely offline.

Has this happened to you? It has not happened to me yet, but I wanted to see how ZFS responded. I have to say I am pretty impressed.

I purposely pulled two working drives from my test zpool array. The status of the pool became Unavailable, as is to be expected. The zpool status command gave a helpful hint “Replace the drive and run zpool clear”

I replaced the last drive I had previously pulled and ran the command:

zpool clear storage

That was all I had to do! The array came back up (although in a degraded state) and all my files were there.

Output of zpool status at this point:

[root@freenas /data]# zpool status
  pool: storage
 state: DEGRADED
status: One or more devices has been removed by the administrator.
        Sufficient replicas exist for the pool to continue functioning in a
        degraded state.
action: Online the device using 'zpool online' or replace the device with
        'zpool replace'.
  scan: scrub repaired 0 in 0h26m with 0 errors on Sun Sep  7 09:51:19 2014
config:

        NAME                     STATE     READ WRITE CKSUM
        storage                  DEGRADED     0     0     0
          raidz1-0               DEGRADED     0     0     0
            ada2p1               ONLINE       0     0     0
            7167795297630497018  REMOVED      0     0     0  was /dev/ada3p1
            ada4p1               ONLINE       0     0     0
            ada1p1               ONLINE       0     0     0

errors: No known data errors

My next experiment was to bring the pool back to full health again. I tried to simply re-insert the last drive into my pool but it complained that it was already a part of the pool. The drive in question used to be labeled ada3p1. I tried “zpool detach storage ada3p1” but it complained: only applicable to mirror and replacing vdevs

After searching I found a mention here that said you can call out specific devices in your pool to clear. I ran the command
“zpool clear storage ada3p1” and it completed without any issues; however it still wouldn’t let me add the drive back into the pool saying it was already there.

What allowed me to bring the array back to full health was:

zpool online storage ada3p1

The amazing part – zfs realized that it only needed to sync a small amount of data to bring it back into sync with the pool!

 scan: resilvered 24K in 0h0m with 0 errors on Sun Sep  7 12:23:39 2014
config:

        NAME        STATE     READ WRITE CKSUM
        storage     ONLINE       0     0     0
          raidz1-0  ONLINE       0     0     0
            ada2p1  ONLINE       0     0     0
            ada3p1  ONLINE       0     0     0
            ada4p1  ONLINE       0     0     0
            ada1p1  ONLINE       0     0     0

Compared to mdadm where it would rebuild the whole array even if it was the same disk you pulled, this is astounding.

I realized that this issue would only happen if you’re putting the same drive you just pulled back into the array, so I then tried pulling a drive and putting another in its place. After partitioning the drive, a simple

zpool replace storage 7167795297630497018 ada3p1

Did the trick (where the string of numbers is the placeholder for the drive you pulled – a zfs status will tell you what that number is.)  Done.

CLI

Watch a zpool resilver in freeNAS

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In my experiments with freeNAS and RaidZ I have come to miss some functionality I enjoyed with Linux and mdadm. One such function was being able to watch an array rebuild, or in ZFS parlance, a pool resilvering.

My inability to watch the resilvering stems from the difference between what the watch command in Linux does and what it does in FreeBSD. Watch in BSD snoops on a tty line whereas watch in Linux executes a command repeatedly.

One option is to install a watch utility for BSD that behaves as the Linux watch command; however, freeNAS is a small read only image so installing things isn’t an option.

The way to do it in freeNAS is to use a while loop in the command line. After 20 minutes of googling I realized that there is no easy way to do this in one line like you can in bash (something about things requiring to be on a new line), so I had to settle for a quick script like one outlined here.

My familiarity with scripts comes from BASH, but I quickly found out freeNAS doesn’t ship with BASH.

echo $shell
/bin/csh

edit: It turns out freeNAS does indeed ship with bash! It’s just not the default shell. Simply execute “bash” in the shell and use your familiar bash shell syntax to your heart’s content. The BASH equivalent of the script below is:

while [ true ]; do clear; zpool status; sleep 1; done

I’ll leave the rest in for reference sake.

I did some digging on how to write CSH scripts and thanks to this website was able to write a simple CSH script to execute a given command at a given interval indefinitely.

Here is my C style watch script:

#!/bin/csh

#A simple script to replace the Linux watch functionality. The first input it takes is how many seconds to refresh; the second, the command to run. If the command has arguments (spaces), it must be passed in quotes.

set INTERVAL = "$1"
set COMMAND = "$2"

while ( 1 )
        clear
        $COMMAND
        sleep $INTERVAL
end

I placed this script in the /tmp directory, made it executable by running chmod +x, and then executing it by running ,/script.sh 1 “command”

CLI

Check hard drives for bad sectors in Linux/BSD

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It turns out that when hard drives fail, they don’t all fail completely. In fact, most fail silently, getting worse and worse as time moves on, causing bitrot and other issues.

I had a suspicion that one of my drives was failing so I thought I would test it. The tool for the job: badblocks.

badblocks writes data to the drive and then reads it back to ensure it gets the expected result. I have learned a lot about hard drive failure lately and now subscribe to running badblocks on every new hard drive I receive to ensure it is a good drive. The command I use is:

badblocks -wsv <device>

This is a destructive write test – it will wipe the disk. You can also run a non-destructive test, but for new disks you can go ahead and wipe them. I also use badblocks to ensure old disks can still be trusted with data. It’s great for “burn in” testing to ensure a drive won’t fail.

Update 3/1/19: If you encounter the following error:

badblocks: Value too large for defined data type invalid end block (5860522584): must be 32-bit value

It means your drive is too big for badblocks to recognize using the default sector size. Fix this by specifying a 4k sector size:

badblocks -b 4096 -wsv <device>

Thanks to Ubuntu Forums for the info.

Networking

Manually install Sophos UTM update

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In the event that you want to install a soft released update to your Sophos UTM appliance before it has been picked up by auto update, you must download and install the patch manually. There is no way to do this in the GUI (yet.) Procedure taken from this helpful post (thanks, heartbleed!)

  1. Shell into the firewall and navigate to /var/up2date/sys 
    cd /var/up2date/sys
  2. wget the patch file (.tgz.gpg extension) 
    wget ftp://ftp.astaro.com/UTM/v9/up2date/u2d-sys-9.205012-206035.tgz.gpg
  3. Invoke auisys.plx with the –showdesc paramater 
    auisys.plx --showdesc
  4. Install the update. 
    cc system_up2date system_update

    Alternatively you can go into the web interface and schedule the install from there.

Easy peasy.

CLI

Creating a ZFS RaidZ volume with different sized disks

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While I hear that “ZFS likes to use the whole disk” I wanted to experiment with creating a RaidZ pool with disks of different sizes. This requires partitioning the larger disks. The GUI in FreeNAS does not allow you to do this, so we must venture toward the command line. While these commands were run in FreeNAS they will work in any FreeBSD based system.

The commands below assume you are using the first four disks in the system for the RaidZ pool. I realize you can make these commands more efficient by using shell-fu but I will put them all here for completeness.

Partition the disks

Create GPT table for each disk

  • gpart create -s gpt ada1
  • gpart create -s gpt ada2
  • gpart create -s gpt ada3
  • gpart create -s gpt ada4

If gpart complains (probably due to the disk already having a GPT table) you can nuke the GPT setup and start over via the following commands, replacing ada2 with the stubborn drive:

  •  gpart destroy -F ada2
  • gpart create -s gpt ada2

Create partition for each disk

  • gpart add -s 232G -t freebsd-zfs -l test0 ada1
  • gpart add -s 232G -t freebsd-zfs -l test0 ada2
  • gpart add -s 232G -t freebsd-zfs -l test0 ada3
  • gpart add -s 232G -t freebsd-zfs -l test0 ada4

Create the pool

  • zpool create storage raidz ada1p1 ada2p1 ada3p1 ada4p1

Why does everyone call their pool “tank”? It must be in some documentation somewhere that everyone copies.

If you want to replace a failed disk in a pool after the faulty disk has been removed, issue the following command:

  • zpool replace storage <old/failed device name> ada2p1

Sometimes even though you’ve nuked the gpt data of the disk zpool will complain about the disk already being a member of a pool, e.g. “/dev/ada2p1 is part of active pool ‘storage'” Another scenario is if you have properly replaced the failed drive but the pool still shows degraded with a hash referring to the old drive showing in zpool status. To fix these issues use the zpool detach command

zpool detach storage ada2p1

 Check pool status

  • zpool status

If it comes out healthy you are good to go.

Import the raidZ into FreeNAS

With the pool manually created you can now import it into FreeNAS so it can be monitored / managed.

  • Click on Storage / Volumes / Auto Import Volume
  • Click No, skip to import
  • Wait a minute for it to scan, then click OK

Done.

Virtualization

Create local storage in Xenserver

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For some reason the default installation of Xenserver on one of my machines did not create a local storage repository. I think it might be due to my having installed over an existing installation of Xenserver and the installer got confused.

I tried manually creating a storage repository by running the following command:

xe sr-create content-type=user device-config:device=/dev/disk/by-id/scsi-SATA_WDC_WD3200AAJS-_WD-WMAV2C718714-part3 host-uuid=9f8ddd87-0e83-4322-8150-810d2b365d37 name-label="Local Storage" shared=false type=lvm

Alas, it resulted in an error:

Error code: SR_BACKEND_FAILURE_55
Error parameters: , Logical Volume partition creation error [opterr=error is 5],

After much googling I came across this page, which has the explanation. Apparently you need to create an LVM physical volume on the desired partition by running the following command:

pvcreate /dev/disk/by-id/scsi-SATA_WDC_WD3200AAJS-_WD-WMAV2C718714-part3

WARNING: software RAID md superblock detected on /dev/disk/by-id/scsi-SATA_WDC_WD3200AAJS-_WD-WMAV2C718714-part3. Wipe it? [y/n] y

It seems the installer noticed an md superblock on this partition and freaked out, hence no local storage. Agreeing to wipe it created the storage repository. One last step: making it the default repository:

xe pool-param-set uuid=<pool UUID> default-SR=<SR UUID>

You can get the pool UUID by running: xe pool-list

Done.

Edit: 10/09/2014

I recently came across a new error message when trying to add a local repository:

The SR operation cannot be performed because a device underlying the SR is in use by the host.

Google searches didn’t reveal much. After a while I realized what was wrong: I had omitted the host-uuid: option. This option is required when you are a part of a pool, but not when you have a standalone xenserver. So, if your xenserver is a member of a pool, don’t forget the host-uuid parameter.

Virtualization

Manually apply patches to Citrix Xenserver

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Citrix Xenserver has many features, all of which are now free as of Xenserver 6.2. XenCenter, however, still expects a support license to use some of its features. One of those features is applying patches. Fortunately it’s easily done via the command line. Their site has documentation on how to do this. Below are my “cliff notes”

  1. xe patch-upload file-name=<filename>
    Note: .xsupdate is the extension of xenserver updates
  2. Wait a moment, then copy the UUID that it outputs
  3. xe host-list
  4. xe patch-apply uuid=<UUID copied from patch-upload>  host-uuid=<host UUID as out put from xe host-list>

If you’re in a pool, instead of xe patch-apply, you can do xe patch-pool-apply <UUID> to apply the patch to all pool members.

Web

Configure SSMTP to use SSL/TLS connections

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SSMTP is a very simple SMTP mail program which is used to send e-mails to a target server. It’s not a fully feature e-mail server but simply passes e-mails on. I first became acquainted with it because it’s the only mail server you can install on Citrix Xenserver. I now use it with all my servers because it’s very easy to configure.

Simply install it via command line:

sudo apt-get install ssmtp

There is only one config file to worry about: /etc/ssmtp/ssmtp.conf. To configure it to use an SSL connection (for gmail or if, like me, your ISP blocks port 25), add the following options, changing the brackets with your mailserver, username, and password.

mailhub=<mailserver>:587
UseSTARTTLS=YES
AuthUser=<username>
AuthPass=<password>
AuthMethod=DIGEST-MD5

If you just pasted the above config into your ssmtp.conf be sure to check the resulting config file for duplicate entries.

It’s as simple as that. All outgoing mail will be sent to the server specified above.

Mobile

Rooting and flashing Verizon Galaxy S4 VRUFNC5

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Below is my experience with rooting and flashing a newer ROM on my Verizon Wireless Samsung Galaxy S4. Thanks to a recently discovered kernel exploit (both scary and awesome) rooting was the easy part. Thanks to the encrypted bootloader on my phone and the KitKat update which made it impenetrable (at least for now) getting a new ROM on the phone was a little more difficult. Thanks to rootjunky.com for the informative video guide.

  1. Root the phone with towelroot.
    Simply navigate to the site, click the lambda to download the towelroot APK, then copy to your device and install it.
  2. Install SuperSU from the Google Play store
  3. Install Android Terminal Emulator
  4. Set selinux to permissive mode
    Open terminal editor and type the following:
    su
    setenforce 0
  5. Install busybox
  6. Install Safestrap 3.72 (the ATT version works fine)
  7. Reboot into safestrap and backup the current ROM (optional, but recommended)
  8. Install ROM of choice via Safestrap on the Stock ROM slot (other slots don’t work as of this writing.)
    I chose the hyperdrive ROM
  9. Flash safestrap KitKat module to fix Wireless functionality
  10. Remove “Press and Hold to add items to launcher screen” by dragging a widget from one screen to another

Success.

Screenshot_2014-08-26-08-36-16