Get Yours Hands Off My HDD
November 1, 2012 2 Comments
Ever since I first had a device boot via SSD, I’ve been a huge fan and proponent. I often say SSDs enjoy the Charleton Heston effect: “You’ll pull my SSD out of my cold, dead hands.”
They’re just absolutely fantastic for desktop operating systems. Nothing you can do will make your desktop or laptop respond faster than adding an SSD for boot/applications. Even a system a couple years old with an SSD will absolutely run circles around a brand new system that’s still rocking the HDD.
And the prices? The prices are dropping faster than American Airline’s reputation. Currently you can get great SSDs for less than $1 per gig. Right now the sweet spot is a 256 GB SSD, though the 480/512 GB are coming down as well.
Desktop operating systems are very I/O intensive, especially with respect to IOPS, and that’s where SSDs shine. Your average 5400 RPM laptop drive gives about 60 IOPS, while a decent SSD gives you about 20,000 (more for reads). So unless you’re going to strap 300+ drives to your laptop (man your battery life would suck), you’re not going to get the same performance as you would on an SSD. Not even close. And it doesn’t matter if you’re SATA 2 or SATA 3 on your motherboard (or even SATA 1), the SSD’s primary benefit of super-IOPs won’t be restricted by SATA bandwidth.
So right now there are two primary drawbacks: Costs a bit more and the storage is less than you would get with a HDD. But boy, do you get the IOPS.
However, lately I’ve heard a few people express hesitance (and even scorn) towards SSD. “When you have an SSD go tits up, then you’ll wish you had a hard drive” is something I’ve heard recently.
Three of the biggest issues I see are:
1: Fear of running out of writes: SSDs have a limited write lifespan. Each cell can only be written to a number of times, and when that limit is reached, the cell is read-only. Modern SSD controllers do tricks like wear leveling
2: Data retrieval: If the SSD fails, there are no methods for retrieving data. There are lots of ways you can attempt to recover data from a failed disk of spinning rust (though nothing guaranteed), but no such options exist for SSDs that I’m aware of.
3: SSDs lie: SSDs do lie to you. They tell you that you wrote to a particular block that doesn’t actually correspond to a physical cell like it would a sector/track on a physical drive. This is because SSDs do wear-leveling, to ensure the longest possible lifespan of the SSD. Otherwise the blocks where the swap is stored would wear out far quicker than the rest of the drive. Our file systems (NTFS, Ext4, even ZFS) were all built on the abilities and limitations of spinning rust, and haven’t caught up to flash memory. As a result, the SSD controller has to lie to us, and pretend it’s a spinning disk.
Here’s a few things to keep in mind.
1: Yes, SSDs have a limited lifespan. The Crucial M4 has a limited write life of 36 TB, which is 20 GB a day for five years. You probably don’t write that much data to your SSD every day. And the worst that happens when your drive reaches the limit is that it becomes read-only. I don’t trust HDDs that are older than 4 or 5 years anyway.
2: True, if your SSD fails, there’s little chance of recovery (while there’s some chance of recovery if it’s a HDD). This highlights the need for a decent backup mechanism. Don’t let the chance that you could retrieve data from a HDD be your backup plan.
3: Yes, SSDs lie. So do HDDs.
I still use HDDs for media storage, backups, and archival. But apps and OS, that’s definitely going to sit on an SSD from now on. It’s just too awesome. And if that means I have to swap them out every 5 years? I’m fine with that.