It has not been true for a LONG time. That was part of Google early “compute unit” strategy that involved things like sealed containers and such. Turns out that’s not super efficient or useful because you leave large swaths of hardware idle.

In my day we had software that would “drain” a machine and release it to hardware ops to swap the hardware on. This could be a drive, memory, CPU or a motherboard. If it was even slightly complicated they would ship it to Mountain View for diagnostic and repair. But every machine was expected to be cycled to get it working as fast as possible.

We did a disk upgrade on a whole datacenter that involved switching from 1TB to 2TB disks or something like that (I am dating myself) and total downtime was so important they hired temporary workers to work nights to get the swap done as quickly as possible. If I remember correctly that was part of the “holy cow gmail is out of space!” chaos though, so added urgency.