In choosing between Raid 1 and Raid 5 configuration for the PR4100 I would like to know that once my volume is degraded due to a single disk failure, can I access my data to copy it to a backup drive before attempting to rebuild the volume on a replacement drive? My understanding is that while I am rebuilding the replacement drive, my volume is not available (for both Raid 1 and Raid 5). Is this correct? I have read that rebuilding can take a long time (days), and I do not want to be locked out of access to my data if possible.
I realize that separate backup is necessary and I intend to use my existing two NAS’s (a 2 TB MyCloud Mirror; and a 4 TB Dlink DNS 343) as backup to my PR-4100. What are the drawbacks you refer to with Raid 1?
In Raid 5, data can be recovered when the Raid is working. Recovery is faster in Raid 1. Recovery is slow in Raid 5 due to parity and calculations for rebuilding the data storage. Raid 1 does not do any error correction and detection whereas Raid 5 has many techniques for error correction and detection.
Yes, your understanding is correct. With both RAID 1 (mirroring) and RAID 5 configurations, once a single disk fails and the volume becomes degraded, you can still access the data on the remaining good disk(s) to copy or back it up before attempting to rebuild the array.
However, during the actual rebuild process when you insert a new replacement drive, the volume will be inaccessible or in a read-only state until the rebuild completes. This is because the RAID controller needs to use the parity information (or the mirror in case of RAID 1) to reconstruct the data on the new drive, which is a resource-intensive process.
The rebuild time can indeed take a long time, especially for larger volumes and depending on the performance of your system. It’s a good practice to first back up your data to another storage device when the volume is degraded, before initiating the rebuild process.
This way, you have a backup copy in case anything goes wrong during the rebuild, and you don’t have to worry about being locked out of your data for an extended period. Once the rebuild completes successfully, you can then copy the data back to the fully rebuilt RAID volume if needed.
