difference between mirror and alternate pv links????

[singvey]

1.I think mirror is that when i read a data block , the system can get from one disk also can get from the mirror disk.That is one data block has another same data block .is this right ??????????


2.I think alternate pv link in lvm is that when read a data block ,the system can go to the disk from one path,also can through another path . That is to one data block with two path. is this right?????????


3.Is this right that the system external diskarray can have alternate pvlink, but the system internal disks directly connecting by internal scsi bus do not have alternate pv link???????

[Florian Heigl (new acc)]

1/2/3 completely right :)

[Pedro Cirne]

Hi,

All your point are right:

1-Yes, you have a mirror when a Logical Extent has 2 or more Phisical Extents, normaly on different disks, but it is possible they are on the same disk.

2-Yes, you can have more than a PV Link to the same disk, you may check that with vgdisplay -v, where phisical volumes are metioned with the Primary and Alternate Links, if they exist.

3-Yes, in most cases, internal disks have just one PV Link.

Enjoy :)

Pedro

[Bharat Katkar]

Hi,
To put it in very simple words:

Mirror: protects from Disk failures

Alternate PV links: Protects from Disk Array link failure (It may be due to HBA/cables/connectors failures)


Regards,

[singvey]

thanks a lot !!!!