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Troubleshooting XenServer deployments

Troubleshooting XenServer deployments. Tomasz Czajka, Sr. Support Engineer 8th of October 2010. Agenda. Case Study: “ Production down” Learn: “ XenServer crash ” Case study: “ Singlepathing ” Q & A. “ Production down”. VM don’t start - why?. Basic troubleshooting in XenCenter.

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Troubleshooting XenServer deployments

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  1. Troubleshooting XenServer deployments Tomasz Czajka, Sr. Support Engineer 8th of October 2010

  2. Agenda • Case Study: “Production down” • Learn: “XenServer crash” • Case study: “Singlepathing” • Q & A

  3. “Production down”

  4. VM don’t start - why? Basic troubleshooting in XenCenter Cannot start a VM“The SR is not available” error Storage Repositry (SR) in “broken” state “Repair” does not work. Use CLI to troubleshoot

  5. SR SR Broken storage # xepbd-list currently-atached=false What is “broken”? PBD PBD PBD = Physical Block Device Volume Group XenServer_1 PBD Name: <Prefix>+SR UUID” SR XenServer_2 PBD has UUID (unique ID) SCSI ID

  6. Storage troubleshooting Goal: Reproduce and analyse the logs /var/log/xensource.log* ;SMlog* ; messages* ; # tail –f /var/log/messages >/tmp/ShortLog # date # echo “Unplugging cable” >> messages messages (UTC) <> xensource.log (local)

  7. PBD unplugged Plugging PBD manually # xe pbd-list host-uuid=... sr-uuid=... # xe pbd-plug uuid=... SR_BACKEND_FAILURE_47: The SR is not available no such volume group: VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4 # xe sr-list name-label=“My SR” params=uuid19856cba-830c-e298-79fa-84a79eb658f4 # grep “PBD.plug” xensource.log

  8. Volume Group 3 VMs 1 virtual disk each Logical Volume Manager (LVM) What is VG? Volume Group(VG) Physical Volume(PV) Virtual Disk Physical Volume(PV) Volume Group(VG) Logical Volume(LV) HDD / LUN VDI Logical Volume(LV) VDI HDD / LUN Physical Volume(PV) Logical Volume(LV) VDI HDD / LUN Storage Repository SR

  9. Volume Group Matching the UUID # vgs # vgs 'VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4' Volume group "VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4" not found VG #PV #LV #SN AttrVSizeVFree VG_XenStorage-090d4717-9f91-92de-83c3-5458274802e9 1 18 0 wz--n- 89.99G 19.48G VG_XenStorage-5239de43-6a74-0365-f825-b799aa6de853 1 2 0 wz--n- 129.07G 129.05G VG_XenStorage-70a029cf-7f35-c035-4af7-07eaf31e2e88 1 11 0 wz--n- 49.99G 2.84G VG_XenStorage-9be18df5-3fd2-4835-b864-d0ffbccbaeb3 1 1 0 wz--n- 1.99G 1.98G

  10. Examining HDD/LUN Checking SCSI ID check SCSI ID (unique for each SCSI device) # xepbd-list params=device-configsr-uuid=... device-configSCSIid: 360a9800050334f49633459 PBD SCSI ID

  11. Examining HDD/LUN Can Linux kernel see this block device? (SCSI device) # hdparm -t /dev/disk/by-id/scsi-360a98045234t654... Timing buffered disk reads: 138 MB in 3.02 seconds = 45.68 MB/sec (LUN readable!  )

  12. Addressing SCSI disks # ls -lR /dev/disk | grep 360a9800050334f4963345767656c546 /dev/disk/by-id scsi-360a9800050334f4963345767656c546a -> /dev/sde /dev/disk/by-scsibus 360a9800050334f4963345767656c546a-1:0:0:5 -> /dev/sdc 360a9800050334f4963345767656c546a-2:0:0:5 -> /dev/sde /dev/mapper/360a9800050334f4963345767656c546 Also check /dev/disk/by-path

  13. Examining HDD/LUN Is the LUN empty? # udevinfo -q all -n /dev/disk/by-id/scsi-360a9800050334f496334576765... ... ID_FS_TYPE=LVM2member ... “If this is LVM member, why there is no VG on it?”

  14. Examining HDD/LUN Is there a VG created on PV? # pvs # pvs |grep 360a9800050334f496334595a32306431 PV VG Fmt Attr Psize Free /dev/mapper/360a9800050334f496334595a32306431 VG_XenStorage-332432-430d-3423-4332434-5485974lvm2 a- 14.99G 14.99G # xesr-list name-label="My SR"params=uuid19856cba-830c-e298-79fa-84a79eb658f4 VG_Xenstorage<UUID> differs fromSR UUID ! PV VG FmtAttrPsize Free /dev/mapper/360a9800050334f4963 VG_XenStorage-090d4717-9f91-92de-83c3- lvm2 a- 89.99G 19.48G /dev/mapper/360a9800050334f4963 VG_XenStorage-70a029cf-7f35-c035-4af7- lvm2 a- 49.99G 2.84G /dev/mapper/360a9800050334f4963 VG_XenStorage-19856cba-830c-e298-79fa- lvm2 a- 14.99G 6.45G /dev/mapper/360a9800050334f4965 VG_XenStorage-9be18df5-3fd2-4835-b864- lvm2 a- 1.99G 1.98G /dev/sda3 VG_XenStorage-5239de43-6a74-0365-f825- lvm2 a- 129.07G 129.05G

  15. No original VG on the LUN Potential reasons: (Re)installation of host in the same pool • Unplug FC / Zoning (Re)installation of host in other pool • Zoning Adding SR with “xe sr-create” in CLI ...BE VERY CAREFUL!

  16. Volume Group ...has been recreated! Lost LVM metadata Lost 100 MB of the VDI data Action steps: don’t shutdown running VMs Online backup for running Vms (now) Block-level clone of the whole LUN (now) Assess professional data recovery

  17. Make a copy first # cp /etc/lvm/backup/* /root/backup/ Volume Group Looking for LVM metadata backup /etc/lmv/backup/VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4 Check backup timestamp (within the file) LVs in backup file # cat /etc/lvm/backup/VG... | grep VHD VDI in xapi database # xe vdi-list sr=<uuid> params=uuid = LV VDI LV VDI LV VDI

  18. Volume Group Removing new VG and PV # vgremove"VG_XenStorage-<new SR uuid>” # pvremove/dev/mapper/<SCSI ID>

  19. Volume Group Recreating PV and VG from backup # pvcreate--uuid<PV uuid from backup file>--restorefile/etc/lvm/backup/VG_XenStorage-<SR_UUID> /dev/mapper/<SCSI ID> # vgcfgrestoreVG_XenStorage-<SR UUID>-f /etc/lvm/backup/VG_XenStorage-<SR UUID>

  20. Examining HDD/LUN Confirm that VG name contains SR uuid... # pvs |grep 360a9800050334f496334595a32306431 PV VG Fmt Attr Psize Free /dev/mapper/360a9800050334f496334595a32306431 VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4 lvm2 a- 14.99G 14.99G # xesr-list name-label="My SR"params=uuid19856cba-830c-e298-79fa-84a79eb658f4 VG_Xenstorage<UUID> matches SR UUID

  21. Logical Volume(LV) Volume Group Checking Logical Volumes # lvs MGTVG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4 -wi--- 4.00M VHD-352d31ec-aeb6-4601-8ea9-990575dab395VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4 -wi--- 520.00M VHD-7e5f83a7-b6c4-4fae-9899-1e6a2cdabd32VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4 -wi--- 4.02G VHD-fbce18dd-397e-444e-9470-b6fa240243d9VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4 -wi--- 4.02G VHD-ff744448-1b7f-4cc8-80b1-cd38b6c90c98VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4 -wi--- 520.00M Logical Volume(LV) Logical Volume(LV)

  22. Storage Repository Plugging PBD again... # xe pbd-plug uuid=… # xe sr-scan uuid=… Error code: SR_BACKEND_FAILURE_46 Error parameters: , The VDI is not available [opterr=Error scanning VDI 7e5f83a7-b6c4-4fae-9899-1e6a2cdabd32] # xe vdi-list uuid=<above number> # lvremove /dev/VG_XenStorage-19856cba-830c-e298-79fa-84a79eb658f4/VHD-7e5f83a7-b6c4-4fae-9899-1e6a2cdabd32 # xe sr-scan uuid=… Success! But no VDIs shown... Success! All VDIs shown... Well done! 

  23. What we’ve learned ...by troubleshooting “Production Down” issue PBD to get plugged needs... LUN/HDD  PV  VG (SR)  LV (VDI) VG name generated from SR uuid (+ prefix)LV namegenerated from VDI uuid(+ prefix) Displaying VG (vgs), PV (pvs), LV (lvs) Addressing block devices (/dev/disk) Examining HDD/LUN with "hdparm –t" Restoring PV & VG from backup

  24. “The XenServer Crash”

  25. The XenServer Crash? Unresponsive orrebooting host Kernel panic or crash dump • Error on Console, host locked • Memory addressing, Bug in OS, Hardware failure No Kernel Panic and no crash dump • Host rebooting / frozen / no errors on the console • Hardware failure, OS busy (I/O), user action

  26. Symptom: Host is unresponsive Symptom: Host rebooted itself Serial console No serial console No crashdump /var/crash/<date> exists Boot the host to the console CTX120540 & reboot Connect local console Review crashdump Generate crashdump CTX120540 & reboot Any errors on the console? HA disabled HA enabled Review crashdump Take photos and reboot Analyse /var/log/messages, xensource.log Disable HA Add „noreboot” option in extlinux.conf Host fenced? Check /var/log/xha.log Analyse /var/log/messages, xensource.log Still rebooting?  examine hardware Analyse /var/log/messages, xensource.log for HA reasons Contact Citrix Tech Support

  27. Getting into details… Analyse /var/log/messages, xensource.log Startup strings: # cd /var/log # grep “klogd” messages -B100 # grep “SERVER START” xensource.log -B100 As easy as grep

  28. Review crashdump Inside crash log directory /var/crash/<stamp> Domain0.log crash.log Domain1,2,3...log Debug.log xen-memory-dump Domain0 console ring Hypervisor console ring HA activity, page fault, driver, storage issues CPU stack - to be analysed by Citrix Tech Support Citrix Confidential - Do Not Distribute

  29. Investigating crash.log Review crashdump (cont) XenConsole ring located at the bottom of the file (XEN) Watchdog timer fired for domain 0(XEN) Domain 0 shutdown: watchdog rebooting machine. Why watchdog triggered?  /var/log/xha.log (Network or Storage heartbeat failed) Why heartbeat failed?  /var/log/messages (DMP, kernel, drivers, I/O errors)

  30. Investigating crash.log Page fault Other examples: (XEN) **************************************** (XEN) Panic on CPU 6: (XEN) FATAL TRAP: vector = 14 (page fault) (XEN) [error_code=0000] , IN INTERRUPT CONTEXT (XEN) **************************************** (XEN) (XEN) Reboot in five seconds...

  31. What we’ve learned Learn: XenServer crash Host really crashed? Kernel Panic Crashdump Triggering Crashdump manually Locating host reboot in the logs Reviewing crashdump logs

  32. “Single-Pathing”

  33. Storage Performance issue DMP has been enabled to improve performance Virtual Machines are running on different iSCSI SRs LinuxGuestVM:~# hdparm -t /dev/xvdb /dev/xvdb: Timing buffered disk reads: 96 MB in 3.07 seconds = 30.41 MB/sec

  34. Storage Performance Checking multipath status # mpathutil status 360a9800050334f496334596c71665246 dm-13 NETAPP,LUN [size=2.0G][features=0][hwhandler=0][rw] \_ round-robin 0 [prio=4][enabled] \_ 3:0:0:2 sdk 8:160 [active][ready] \_ 4:0:0:2 sdj 8:144 [active][ready] /dev/mapper/.... /dev/

  35. Storage Performance Determining current performance on domain0 Testing multi-path device # hdparm /dev/mapper/<scsi id> Testing single-path devices # hdparm /dev/sdj # hdparm /dev/sdm In all cases: 30 MB/sec

  36. Storage Performance Determining usage of paths # iostat –x <device> # iostat –x/dev/sdk /dev/sdj 5 Device Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sdk 803.50 33.0 4122 160sdj 784.00 32.83922 155 Both paths are used equally

  37. Storage Performance Checking if there are really 2 iSCSI sessions # ls -alR /dev/disk/by-path/ | egrep "(sdk|sdj)" ip-10.1.200.40:3260-iscsi-iqn.1992-08.com.netapp:MyNetapp.luns-lun-2 -> ../../sdk ip-10.1.201.40:3260-iscsi-iqn.1992-08.com.netapp:MyNetapp.luns-lun-2 -> ../../sdj

  38. Storage Performance Checking if different paths are really used # tcpdump -i any port 3260 # watch "ifconfig | egrep '(eth0 |eth1 )' -A5 | egrep '(eth|bytes)' " eth0 Link encap:Ethernet HWaddr 00:1D:09:70:88:2C RX bytes:1490076463 (1.3 GiB) TX bytes:170615419 (162.7 MiB) eth1 Link encap:Ethernet HWaddr 00:1D:09:70:88:2E RX bytes:1801238 (166 MiB) TX bytes:46695876 (44.5 MiB)

  39. Storage Performance Checking source IP addresses for iSCSI sessions # netstat -at | grep iscsi 10.1.200.138:53049 10.1.200.40:iscsi-target ESTABLISHED 10.1.200.178:46684 10.1.201.40:iscsi-target ESTABLISHED

  40. Storage Performance Checking kernel routing table # route Destination Gateway Genmask Iface 10.1.200.0 * 255.255.255.0 xenbr0 10.1.200.0 * 255.255.255.0 xenbr1 default 10.1.200.1 0.0.0.0 xenbr0

  41. Storage Performance Configuration of management interfaces in XenCenter Modify ISCSI_2 into 10.1.201.78

  42. Storage Performance Determining current performance on domain0 # route Destination Gateway Genmask Iface 10.1.200.0 * 255.255.255.0 xenbr0 10.1.201.0 * 255.255.255.0 xenbr1 default 10.1.200.1 0.0.0.0 xenbr0

  43. Storage Performance Configuring kernel routing table ...or (not recommended) Add to /etc/rc.local # route add -host 10.1.200.40 xenbr0 # route add -host 10.1.201.40 xenbr1 What about Pool Upgrade and Pool Join?

  44. Storage Performance Determining current performance on VM LinuxVM:~# hdparm -t /dev/xvdb /dev/xvdb: Timing buffered disk reads: 45 MB/sec Well Done!

  45. What we’ve learned Case study: Single-pathing /dev/ locations for single and multi-path devices # mpathutil status # hdparm –t # iostat # ifconfig, # tcpdump, # netstat, # route # watch Best practices for iSCSI storages

  46. Questions

  47. Resources First aid kit http://docs.xensource.com –XenServer documentation http://support.citrix.com/product/xens/ - Knowledge Center http://forums.citrix.com/support - Support forums http://community.citrix.com/citrixready/xenserver - XenServer Central (one-stop information center)

  48. Session surveys are available online at www.citrixsynergy.com starting Thursday, 7 October Provide your feedback and pick up a complimentary gift card at the registration desk Download presentations starting Friday, 15 October, from your My Organiser Tool located in your My Synergy Microsite event account Before you leave…

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