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Posts Tagged ‘storage’

Xenserver hosts in halted mode (part 2)

Jul 29, 2012 1 comment

I recently encountered a problem where one server in a pool had shutdown expected in a way which cased the vms running on that host to fail. We restarted the host and found that about half of the vms returned to the pool and could be started on another pool member, however a handful of vms were unable to start. Using information I have previously posted, I checked the power-state for these vms and they were in a halted state. However they were not available in the list_domains command. Further attempts at recovery had failed.

At that point we took a closer took at the system and discovered that the dom0 drive had zero free disk space by running the command df from the console. I connected using winscp and browsed to the log directory and deleted a majority of the old and large log files, which freed up over 59% of the disk space. Another reboot later and the disk space issue was resolved,

However in this case, there was a second issue, which is that the host that was in this state was hosting the Citrix license server and this specific host was unable to contact the license server so it couldn’t start vms. But since this vm was halted instead of stopped I couldn’t start it on a different host yet. Simply going into the license manager in XenCenter, I removed licensing on the host, which placed it into a 28 grace period. Once this was completed I could restart the halted vms, and then subsequently repoint the host back to the license server to remain the Enterprise License feature set.

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70-290 Concepts: Storage

graduation·          Basic Disks use partitions, not volumes, and they can store up to four primary partitions, and one extended partition with logical drives

·          Dynamic Disks use volumes, not partitions, and you can create: simple, spanned, striped, mirrored or RAID-5 volumes.

·          You can use either the Disk Management console or the diskpart.exe utility to work with disk storage.

·          FAT32 (vs FAT) requires W95 OSR2 or higher, increases bits, supporting 2TB, less slack space.

·          Only Windows 2000 (Server/Professional) or higher support dynamic disks.

·          Only Windows Server 2003 and 2000 support striped, mirrored and RAID-5 dynamic disks

·          You can convert a basic disk to dynamic, however converting from dynamic to basic will result in data loss

·          You can use convert c: /fs:ntfs to convert a FAT to NTFS filesystem.

·          When moving disks to another Window Server 2003 Computer, choose rescan from the menu bar in Disk Management; right-click on any disked marked foreign and select Import Foreign Disks.

·          Using diskpart.exe, you can extend a basic partition, but it must be formatted as NTFS and the free space must be contiguous.

·          Spanned volumes cannot be mirrored or striped, and spanned volumes are not fault tolerant

·          Boot volumes, system volumes, striped volumes, mirrored volumes, and RAID-5 volumes cannot be extended (spanned)

·          The boot partition or volume is the drive letter where the Windows Server 2003 operating system files are stored (i.e. c:\windows). The system partition or volume is where the system startup files are stored (i.e. ntldr, ntdetect.com ntbootdd.sys and boot.ini). This is the reverse of the “logical” answer!

·          Spanning uses two or more separate physical dynamics disk to increase the storage capacity of a single drive. Data is written in a linear method, not storing on the second drive until the first is full. Benefit of increased logical storage. No fault tolerance or performance increase.

·          RAID-0 (Striped) use two or more separate physical dynamic disks to store alternating bits of data (striped). This permits the logical drive to equal the total size of all drives, as well as increasing read and write speeds. To repair: install new disk, upgrade to dynamic, delete volume, create new volume, restore.

·          RAID-1 (Mirror volumes) use two separate physical dynamic disks to store identical (mirrored) copies of data, simultaneously, creating redundancy – total storage equals the size of the smaller drive. To repair: install new disk, update to dynamic, break mirror, right-click on new drive – “add to mirror”

·          RAID-5 (Striping with Parity) use of 3 or more (32 max) physical dynamic disks to store data stripped across multiple drives, with a ‘parity’ bit written to the alternate drive. The loss of a single drive is recoverable, the loss of 2 or more drives is unrecoverable – total storage equals the total of all drives minus 1 drive. There is a slightly performance degradation in write operations due to this process.

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