Large drives & rebuild times + URE

[Enquiries]

Dear Sir,

I've seen your YouTube video concerning large vs small drives with a lot of interest. I was hoping to find an answer to the issue of VERY long rebuild times on RAID5/6 systems with very large drives. In this rebuild period your array is very vulnerable, and a few URE's can make the entire RAID corrupt. I even think there is a graph, where it's pointed out that RAID 5 is no longer considered 'safe' when using large drives. As I'm about to upgrade my system to a 12 bay Synology NAS, I want the safest setup possible. Currently I'm using RAID 6, but is this still safe when using >20TB drives? Should I be considering other options like RAID 10 or ZFS or ... ?

I'm also using RAID scrubbing which is is a solution to prevent URE's I guess? And I also have an old NAS to backup the main system. I know RAID is not a backup, but it would be a real big bummer if the RAID system crashes during a rebuild.

Thanks,
Mark

[ed]

You are correct that with very large drives, the rebuild times on RAID 5/6 systems can be very long and leave the array vulnerable to UREs (unrecoverable read errors) that can cause data loss. The general rule of thumb is that the larger the drives, the less safe RAID 5 becomes. With drives over 10TB, some experts recommend avoiding RAID 5 altogether due to the higher probability of encountering UREs during rebuilds.

RAID 6 provides an extra level of protection with two parity drives, but it is still susceptible to UREs during rebuilds, especially with large drives. RAID 10, on the other hand, offers better performance and reliability than RAID 5/6, as it involves striping data across multiple drives in a mirrored configuration, so you have multiple copies of the data. However, it does come at the cost of reduced storage capacity.

ZFS is another option that provides enhanced data protection, as it offers features like checksumming, which can detect and correct data corruption. It also offers a variety of RAID configurations, including RAIDZ, which is similar to RAID 5/6, but with better reliability and faster rebuild times.

In terms of backup, RAID scrubbing can help to detect and correct errors in your RAID array, but it is not a replacement for a proper backup. It's always a good idea to have a backup system in place, such as an old NAS, as you mentioned, or an offsite backup solution like cloud storage.