I know, that it's recommended to put data and log devices on separate disks. Some say it's for security reasons, others say it's for performance.
But, is this "old truth" still valid for external redundant disk arrays ?
With proper point-to-point architecture, there should be no reason for decreased performance with all the devices placed on the same RAID group. And for security - I don't see the advantage of separate disks - if one of them fails, you have to use your backups, so there's no difference, whether you still have half of your devices available.
If I have 8 disks, is it better to create 2 separate RAID10 groups, each with 4 disks and put data on one and log on second ? Or is it better to create one big RAID10 with 8 disks and put everything on it. AFAIK RAID10 on 8 disks should be approximately 2 times quicker on both read and write operations than RAID10 on 4 disks.
So, would you still recommend to place data and log devices on separate RAID groups on external redundant disk array (like Dell/EMC CX3-20 or IBM DS4700) ?