Veritas™ Volume Manager Administrator's Guide Thesoftwaredescribedinthisbookisfurnishedunderalicenseagreementandmaybeused only in accordance with the terms of the. In most cases once the disk (mirrored) is failed means its almost out of the veritas control (technically not) most case standard pratcie is to replace the disk, run devfsadm, label and use vxdiskadm option 5 which will replace the disk automaticlly and resync's unless if there is fibre channel use luxadm commands, etc. If disk was in use & something happened to private region where vxvm is unable to read the disk private region, in this case, you should see disk going in 'failed was' state in vxdisk list. In most of the case, you need to a bottoms up analysis & find what happened underneath to the disk.
- Veritas Vxvm Log
- Veritas Vxvm And Systems Integration
- Veritas Vxvm Download
- Veritas Vxvm Commands
- Veritas Vxvm
Veritas Vxvm Log
VxVM Tutorials
Let us now see different volume layouts that can be created in veritas volume manager. Before diving deep into the RAID levels first create a Disk group with 4 disks. To do this we have to initialize 4 disks to take them under VxVM control.
After this create the disk group mydg with these four disks by naming them from disk01 through disk04.
To confirm the disk group creation check the disks in the disk group mydg:
Concatenated Volume
As shown in the diagram below, in RAID 0 concat volume data is first written linearly in disk01 and then to disk02. Number of subdisks in a concat volume depends upon the size of the volume. IF you have a volume greater than the size of a physical disk you would have a single sub disk on one physical disk and another sub disk on the next physical disk. Remember that the number of sub disks also depend on other factors too. The disadvantage of concat volume is that, it does not provide any redundancy to the data as we always have only one copy of data at a time. Minimum disks required to create a concat volume is 1. Command to create a concat volume :
To print the layout of myvol :
RAID 0 (striped volume)
In this case we spread the data out to multiple disk by creating equal sized columns on each disk. Each column will be on a separate disk. Similar to concat volume a stripped volume also do not provide any redundancy to the data as it has only one copy of data at any point in time. To create a stripped volume you need atleast2 disks.
Now you can specify how many columns you need to stripe out the data. Also you can mention the stripe unit.
Mirrored layout (RAID 1)
Mirrored layout or RAID 1 layout is one of the most commonly used layout in production environments. RAID 1 simply mirrors all the data from one disk to another so that we have an extra copy of data. This provides us the necessary data redundancy. Here each plex is on a different disk. Command to create a RAID 1 mirrored volume is :
To check the layout of a RAID 1 mirrored volume :
RAID 5
In case of RAID 5 volumes a parity information is stored on every disk as shown in the diagram. Now this parity can be used in case you want to recover the data lost due to a disk failure. The parity is spread across all the disk to ensure that we have sufficient copies of parity all the time. We need atleast 3 disks to create a RAID 5 volume. Command to create a RAID 5 volume is :
To check the layout of a RAID 5 volume :
Advantages and disadvantages of various RAID levels
| Concat | RAID 0 (striping) | RAID 1 (Mirror) | RAID 5 | |
|---|---|---|---|---|
| Advantages | 1. Easy to administer 2. Maximum utilization of disk space 3. Any size disks can be added to create volumes. | 1. Parallel data transfer to improve write speed. | 1. Protection against disk failure 2. Faster write performance | 1. More usable disk space than mirroring 2. Redundant 3. Fast read 4. Faster recovery through parity. |
| Disadvantages | 1. No redundancy | 1. No redundancy | 1. Requires more disks to configure 2. A bit slow write performance. | 1. Slow write due to parity. 2. Poor performance after disk failure. |
Mirror-stripe (RAID 1+0)
In case of a stripe mirror the data is first mirrored and then the mirrored data is striped as shown in the diagram. This requires atleast 4 disk. Command to create a mirror-stripe is :
To print the layout of a mirror-stripe volume :
Mirror-concat (RAID 0+1)
Now in case of a mirror-concat volume, the data is first concatenated and then this concatenated data is mirrored as shown in the diagram. This requires atleast 4 disks. To create a mirror-concat volume :
To print the layout of a mirror-concat volume :
Comparisons of various RAID levels
| concat | stripe (RAID 0) | mirror (RAID 1) | RAID 5 | RAID 1+0 and RAID 0+1 | |
|---|---|---|---|---|---|
| Minimum number of Disks required | 1 | 2 | 2 | 3 | 4 |
| Data Protection | no | no | yes | yes | yes |
| Disk space usage (Using minimum number of disks) | 100% | 100% | 50% | 67% | 50% |
| Read performance | High | High | High | High | High |
| Write performance | High | High | Medium | Low | Medium |
Veritas Vxvm And Systems Integration
Layered volumes
Layered volumes are actually built on top of other volumes. In layered volumes data is mirrored at sub disk level which brings in more granularity. Now to do this VxVM creates sub volumes from traditional volumes. Advantages 1. Faster recovery from failure than RAID 1+0 and RAID 0+1 2. Can persist more disk failures than RAID 1+0 and RAID 0+1 Disadvantage 1. Requires more VxVM objects ( sub volumes are required for a layered volume)
1. concat-mirror
In case of concat-mirror, sub disks are concatenated to create the plexes for the sub volumes. The sub volumes are the mirrored to create the top level plex and eventually top level volume. Advantage Recovery is faster as each portion of concatenation is mirrored separately Command to create a concat-mirror volume :
Check the layout of the volume we just created. You should see 2 subvolumes with 2 volumes each. Each volume will have one plex with one sub-disk.
2. stripe-mirror
Veritas Vxvm Download
In case of stripe-mirror, sub disks are mirrored to create the plexes for the sub volumes. The sub volumes are then striped to create the top level plex and eventually a top level volume. Advantage More tolerant to faults, as each stripe is mirrored separately. Command to create a stripe-mirror volume :
Veritas Vxvm Commands
Check the layout of the volume we just created. You should see 2 subvolumes with 2 volumes each. Each volume will have one plex with one sub-disk.
Veritas Vxvm
I hope the post was informative, Do subscribe to stay updated.