RAID 5 with big SATA disks. Do or don't?

You had me a R5 - don't.

The reason is that in the event of a disk failure you have zero protection until you've replaced the disk and the array has rebuilt.

For large cheapo SATA disks this rebuilt process can take DAYS - meanwhile you are at the mercy of a second disk failing - at which point it's game over.

Also this type of disk is rarely happy to work solidly 24 hours a day and I've seen rebuilds kill disks - again making the whole thing rather dubious.

If you can use RAID 10 over 5 or 6, if you insist on 5/6 then use 'enterprise' disks capable of a 24/365 duty cycle.

Using RAID5 with this configuration, you introduce additional risk to your RAID. With the storage density introduced with modern disks, the likelihood of encountering a bad block on multiple disks is higher.

If using 1TB+ disks, it's recommended to use a RAID6 as opposed to RAID5, as it has an additional parity disk.

If you want greater speed as well as better guaranteed availability, you might consider RAID 1+0 as well.

As far as speed, compare the seek time and various other specifications. Speed does not vary much with commodity disks that are higher density. When I bought disks a few months ago, the largest tier1 SAS disk I could buy was 450GB.