PVG x Stripe

[Andre Augusto Ferreira]

Hello people, how you doing?

Can anyone tell me what's exactly the difference between PVG and Stripe?

Another point, I've heard that the performance degrade when File System is created with stripe using meta disks stripe in the storage, is that true? Why?

I hope that my english be understandable.

Thank you very much

André

[RAC_1]

PVG stripe - you form a group pvs and create lvol in that pv group. With pvg lvols, you can mirror. Use /etc/lvmpvg file and options -g to lvcreate.

Strippping
Use of options -i and -I. you strip an lvol over the disks and you can choose the strip size. you can mirror a lvol created with -i and I options.

Also, why would you want to strip twice. Depending upon the raid level you use, the disk coming from SAN/NAS is already stripped. So strippping it again, is not going to help and may even add to slower response and system overhead.

[Senthil Kumar .A_1]

Hi,

There is no direct bearing of PVG strict allocation on neither stripe created using "-i / -I" with lvcreate (block striping) nor the distruted allocation/Extent striping which is created with option "-D" with lvcreate command. The PVG strict allocation has direct bearing on Mirror allocation.

There is only one special case where this has a direct bearing on Striping. especially in extent stiping (-D) option. Thats because we have a case wherein we would be interested in mirroing the stiped volume. read the following quote from man page..

QUOTE

The distributed allocation policy REQUIRES the PVG-strict allocation policy ( -s g ) to ensure that mirrors of distributed extents do not overlap (for maximum availability).

QUOTE END..

By defining a PVG group in /etc/lvmpvg, we define a logical group (Mind you LOGICAL) of the disks that are connected to different controller. By this, when we create a LV with the command "lvcreate" along with the options "-m"(mirror) and if "-s g" used to turn on "PVG strict allocation", the LVM subsystem will make sure the extents are choosen from the disks that belong to different PVG group.

So "PVG" group has only direct bearing with mirror allocation policy not with Striping.

Regards,
Senthil Kumar .A