SSD types and terminology

sample SSD types

• 3.84TB SSD SAS RI 24Gbps FIPS 512e 2.5in Hot-Plug

• 3.84TB SSD SAS RI 24Gbps 512e 2.5in Hot-Plug, AG Drive 1DWPD

• 3.84TB SSD vSAS Mixed Use 12Gbps 512e 2.5in Hot-Plug ,AG Drive SED, 3DWPD

• 3.84TB SSD SAS MU 24Gbps SED FIPS-140 512e 2.5in Hot-Plug 3DWPD

SED - "Self Encrypting Drive". That may or may not mean that data on the disk is encrypted by the drive controller itself, and it may or may not mean that when you "securely dispose" of the drive by selling it on eBay the new owner will have some difficulty accessing all of your information.

FIPS - "F*** IT, PLEASE STOP". An Information Processing Standard used by the US Federal Government to make encryption as difficult to use as possible. Under certain circumstances you will be required to only use FIPS certified hardware, so if you have already fallen for using an SED, this will specify just what encryption methods are used. If you don't NEED it, don't use it.

"512e" - "512 Byte Emulation". New hard drives are designed with 4096 byte sectors, but old drive controllers still think that sectors can only be 512 bytes, so a 512e drive pretends that that is still true. Data is actually written on the disk in 4096 byte sectors but the host addresses them as though they were 512 bytes long and there are eight times as many. It's like LBA for this century.

"AG" - "AGnostic Drive". Yeah, we know that you think that drives from certain manufacturers are better than others, which is why Dell will cover up the nameplate with an "AG" sticker so you can't tell how bad it's going to be until long after you buy it. The idea is that multiple makes of drive will be sold under the same "AG" label and they will all have the same performance specs so it won't matter who makes them. You may think differently when they start failing and you don't know why.

"1DWPD" - "One Disk Write Per Day". If the disk is one terabyte in size and it is rated for 1DWPD, you can write one terabyte to it every day, day after day, for the entire warranty period and it will be fine. 3DWPD would be three terabytes, and so on.

"RI" - "Read Intensive". The drive is optimized for reading a lot at the expense of write performance. Contrast this with "Write Intensive" where you can write a lot but reading will suffer and "Mixed Use" where everybody suffers no matter what they're doing. If you want people to be very impressed with how much research you're doing you can carefully investigate exactly what kind of operations each server will be doing and then choose just the right drive for each one. This will, of course, make no difference at all in three months when the read-only database turns into a logging server and the disk array with the top of the line write intensive drives is only used to store nightly backups.