Do rackmount servers need to be in a rack?
You don't necessarily need a rack or cabinet. Some points to keep in mind though:
- If you keep it under your desk it will accumulate dust.
- The fans of such servers can be rather loud (edit: put mildly! You really don't want that near you all the time!)
- The power consumption might be much higher than that of a SOHO NAS box.
- Rackmountable servers come 19" wide and might be twice that in length.
- If you get an old server with parallel SCSI (not SAS) you will not be able to easily put in SATA-HDDs for regular SOHO-NAS Systems.
- Upgrading parts might be more difficult since they use server hardware (RAM, CPU, HDD etc).
A rack has the advantage that you can mount more than 10 servers in a single rack easily and if you have them on rails still be able to access them (slide out, open up, swap parts etc.). Also cable management, airflow management and power distribution come to mind.
Basically, rack is just a... a rack. Just a metal construction to put hardware in some compact and standardized manner. It may have walls and doors, power distribution units, cable organizers, coolers and other stuff, and may not.
So, the rack is not mandatory to place rackmount hardware. Feel free to put your server anywhere you want (but not to the place where you'll not put any other computer).
Servers, of course, have their own cooling systems. Keep in mind that 1U and 2U cases often have very noisy coolers, and it's not very good decision to put them near your workplace.
A rackmount server need not be physically installed in a rack, but there are several important considerations when operating one at home.
As far as I can tell, there is no regulatory or other requirement for a rackmount server to be installed in a rack. I've seen rackmount servers operated on a table at my college.
As others have noted, thermals can be an issue, so be sure to provide plenty of ventilation in front of and behind the system case. Cool air is taken in from the front and hot air is expelled from the back.
Rackmount servers also tend to have very noisy fans, especially compact 1U models which need to move lots of air within a constrained chassis. I've experienced it firsthand and know how loud these things get. You do not want to be sitting near them.
- For comparison with a consumer part, a rackmount server running under a moderate load with good ventilation is typically at least as loud as a reference AMD Radeon R9 290X graphics card with the fan running at 100%, which is about 65 dBA. Expect even more noise under suboptimal operating conditions, potentially up to 75–80 dBA. Many older models may not have automatic fan speed control at all and therefore always operate at the maximum noise level.
Rackmount servers are ultimately not designed for home use.
You should bear in mind that by their very nature, rackmount servers are not designed to be operated in any sort of residential setting. In fact, some rackmount servers may be illegal to sell for use in a home environment (at least in the United States) because they are FCC Class A devices and emit too much electromagnetic radiation, to the point where harmful interference to electronics may result (emphasis added):
Server and Switch Information - This device has not been approved by the Federal Communications Commission for use in a residential environment. This device is not, and may not be, offered for sale or lease, or sold or leased for use in a residential environment until the approval of the FCC has been obtained. Source
FCC, Class A
This product has been tested and found to comply with the limits for a Class A digital device pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment. This product generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with the manufacturer’s instruction manual, may cause harmful interference with radio communications. Operation of this product in a residential area is likely to cause harmful interference, in which case you will be required to correct the interference at your own expense. Source
A more appropriate solution is a tower case with multiple hot-swap bays. These cases are designed for use in a SOHO environment, and make a lot more sense than a rackmount server if you're trying to build a storage server for home use.