elements of programming interviews errata

The SATA SSD itself is eventually going to disappear (to be replaced by NVMe SSDs), but they should still be around a decade from now when I need replacement drives. In the future, when a drive dies on the array, I’ll likely have to replace it with an SSD, because a replacement spinning disk is no longer available. For right now, they are a lot cheaper than SSDs, a fifth of the price. Thus, the 2.5 inch form factor for spinning disks is likely dead. Also as you know, laptops have moved away from rotating disks, adopting SSDs instead. On a cost-per-gigabyte, the larger drives seem to be best price.As you know, there are only three manufacturers remaining for spinning rust drives: Seagate, Western Digital (WD), and Toshiba.

You don’t have to fill up the system, or buy the largest drives, but if you put in the time and effort, you might as well go all the way.

Buying 6 of them is your largest investment. A 5TB spinning disk costs ~$150, or an 8TB SSD flash costs ~$700. Otherwise, you should buy one of the larger (much larger) system that’ll holder standard sized drives.The drives will be largest cost. Here are all the components of my system:$500 – DS620slim unit$1000 – 6x Seagate Barracuda 5TB 2.5 inch laptop drive (ST5000LM000)$100 – 2x Crucial 8GB DDR3 SODIMMs (CT2K102464BF186D)$30 – 2.5gbps Ethernet USB (CableCreation B07VNFLTLD)$15 – Noctua NF-A8 ULN ultra silent fan$360 – WD Elements 18TB USB drive (WDBWLG0180HBK-NESN)You can save a bunch of money by going down to 4TB drives (and a 14TB backup USB drive), but I chose the larger 5TB drives.Disk DrivesThe most important reason for choosing this product is the smaller 2.5-inch disk drives (sized for laptops). For example, eventually a disk will fail and I’ll have to replace it, and I know now that this is something that will be effortless when it happens in the future, without having to relearn some arcane Linux commands that I’ve forgotten years ago.Despite this, I’m a geek who obsesses about things, so I’m still going to do possibly unnecessary things, like upgrading hardware: memory, network, and fan for an optimized system. I can setup tasks to run on regular basis that would break if I tried to regularly run them on a laptop or desktop computer.There are lots of do-it-yourself solutions (like the Radaxa Taco carrier board for a Raspberry Pi 4 CM running Linux), but I’m choosing this solution because I want something that just works without any hassle, that’s configured for exactly what I need. Spending $500 just for a box to hold the drives is a bit expensive, but the advantage is that it’s also a server that’s powered on all the time. But amortized for the expected 10+ year lifespan, I’m paying $15/month for this home system.This unit is not just disk drives but also a server. In my case, I’m spending $1500 for a 18-terabytes of disk space that would cost only $400 as an external USB drive. My older NAS is 10 years old and I’ve replaced all the disks, one slot replaced twice.This can be expensive. A NAS requires a separate box in addition to lots of drives. With occasional replacements (as failures happen) it can last decades. You simply buy a new disk to replace the failed one and keep going. If you want to keep things, like photos, for the rest of your life, you need to do something different.The solution is RAID, an array of redundant disks such that when one fails (or even two), you don’t lose any data. A failure is unlikely tomorrow, but a spinning disk will almost certainly fail some time in the next 10 years. If you stick a USB external drive on your desktop for backups, it’ll eventually crash, losing any data on it.

It makes this a tiny server that you can hold in your hand.The purpose of a NAS is reliable storage. It’s a “NAS” (network attached storage) server that has six hot-swappable bays for 2.5 inch laptop drives.That’s right, laptop 2.5 inch drives. Mostly these are notes for myself, so when I need to replace something in the future, I can remember how I built the system. In this blogpost, I describe the Synology DS620slim.

Elements of programming interviews errata