This article will talk about Proactive Copy (PACO).

Proactive Copy (PACO) feature will allow disks to actively copy the data to the hot spare. It is triggered by the number of existing media errors on the disk. PACO reduces the possibility of two bad disks existing because it identifies whether a disk is about to go bad and proactively run a copy of the disk.

If the PACO of a disk in the RAID group is broken, we can still use the other disks in the RAID group to calculate the data on bad disk.

There is also something called the PACO-R (Resilient) which can reduce the possibility of having more than two bad discs and will allow for more data copies. EMC recommends that all customers upgrade to PACO-R, especially with Viper-C disk enclosures.

About PACO:

Since December 2006, we can take the initiative to copy the disk to the hot spare disk, and then replace the disk. Prior to this, we can only remove physical disk to rebuild a disk. In the process of rebuilding, the entire RAID group is at risk. So, PACO has three major advantages:

1.     To avoid the incorrect disk error caused by the medium error in the rebuilding process.

2.     Greatly reducing the RAID group having two bad disks.

3.     Performance improvement - the process of coping to the hot spare is a lot faster than the rebuilding process.

Copy to the hot spare is how it works?

The first step is to copy all the data of replaceable disk to an idle hot spare. In this process, the enclosure will be displayed to a transitioning state. When all copies of the data are completed, the disk will be powered off and will be displayed as a bad disk. Then we can safely replace the disk and an equalization process begins. The hot spare data will be copied to the new replacement disk. Then, the machine will display a transitioning state. When equalization process is finished, the hot spare will again enter into an idle state. When we want to replace the disk that is being copied to hot spare, this disk is still maintained in an I/O state. When it maintains the I/O state and you encounter an I/O error in the sector caused by a media error, the system will try to remap the sector. During the PACO process, if a media error and continuing reports reached the limit of bad disk, then this disk will stop PACO and then the rebuilding process will operate on the hot spare disk. If in the rebuilding process, another disk in same RAID group is broken and there are two disks that are broken in a RAID group, it will cause the data unavailable (DU) or data loss (DL).

PACO-R:

PACO-R can prevent the occurrence of two bad disks in a same raid group if disks continue to report media errors. For Hitachi 600G disk's vulnerability on VNX models, EMC offer PACO-R installation to customers. PACO-R version is compatible with VNX Block OE R32 P209, R32 P215, R32 P217. In the R32 P217 and R32 P218, PACO-R is already enabled.

How to install PACO-R:

We have an "ndu" file that is able to install PACO-R directly. It can be installed through USM or the CLI of Control Station. The whole installation process will last for only 2-3 minutes (excluding check time after the installation), and there is no downtime.

Our Remote Proactive team also supports PACO-R installation. If you need to install PACO-R, please feel free to contact RemoteProactive@emc.com to request for an installation.

Please contact us if you have any questions:

E-mail: RemoteProactive@emc.comRemoteProactive@emc.com

Phone: + 1-800-782-4362 x 6305555

On-line support (Live chat): https://support.emc.com

Author: Leo