Question & Answer
Question
Does LVM on AIX support using SSDs?
Answer
SSDs and AIX LVM
Starting in AIX 6100-06 and 7100-00 LVM provides support for Solid State Drives (SSD). These drives are composed of memory (usually NAND-based flash memory) where the data is stored. They do not contain a typical platter, head, armature and circuitry to drive them as hard drives do.
SSDs can provide higher performance due to the lack of mechanical parts, and faster access of data in flash memory.
Note that in an LVM RAID configuration (such as mirroring or RAID 1) I/O operations may not return until they are complete on ALL drives. In this case adding an SSD to a volume group with slower disks will not increase performance.
LVM makes no attempt to optimize performance based on the speed of individual devices. This is left up to the system administrator.
Volume Group Restriction for SSDs
A volume group can be created or changed to specifically restrict it to only allow SSD drives.
In the above versions of AIX a new attribute (-X) has been added to allow LVM to restrict it to only include SSD drives.
- # mkvg -X SSD ...
# chvg -X SSD ...
If the "-X SSD" physical volume restriction is set, LVM will check the existing PVs in the volume group, and will give an error if any do not meet this condition.
- # chvg -X SSD datavg
0516-1930 lchangevg: PV type not valid for VG restriction.
Unable to comply with requested PV type restriction.
0516-732 chvg: Unable to change volume group datavg.
# mkvg -X SSD hdisk27
0516-1254 mkvg: Changing the PVID in the ODM.
0516-1930 mkvg: PV type not valid for VG restriction.
Unable to comply with requested PV type restriction.
0516-1397 mkvg: The physical volume hdisk27, will not be added to
the volume group.
0516-862 mkvg: Unable to create volume group.
The physical volume restriction can also be lifted by using "none" as the physical volume type. This is the default for mkvg.
- # chvg -X none ...
Volume Group Incompatibilities
When this restriction is enabled the volume group will not be able to be accessed by a system that does not support PV restrictions. Even if the restriction is reversed and "none" is used the volume group will not be able to be imported in a system running a lower version of AIX. This is because the volume group version ID is permanently changed when -X is used, and will be incompatible with systems using older versions.
This may be an issue in situations like:
- - A cluster of AIX nodes where not every node is at the same level of OS
- A volume group is exported from the current host and imported into a system with a lower level of AIX.
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Document Information
Modified date:
17 June 2018
UID
isg3T1018986