Switch Your Databases To Flash Storage • Hacker News Board

Re: Switch Your Databases To Flash Storage

#21

Post by kyrra » Mon, Dec 10, 2012, 7:36 PM UTC

bunderbunder wrote: post #14

Wear patterns and flash are an issue, although rotational drives fail too. There are several answers. When a flash drive fails, you can still read the data. A clustered database and multiple copies of the data, you gain reliability – a server level of RAID. As drives fail, you replace them. Unlike magnetic disks, SSDs have a tendency to fail at a really predictable rate. So predictably that if you've got two drives o…

I bet you could setup your drives to fail in a set pattern. Lets say you had 4 drives in a RAID-10. If they were all fresh, swap out the first 2 drives when they are at 50% wear... then on you could swap them out back and forth as they approach 100% wear.

Since they lifespan of some of the drives (Intel and Samsung I believe) is reported in the SMART data, you could easily do this.

SSD drives with SLC memory (enterprise SSD) have 100,000 P/E cycles, so they should last a while unless you are writing just a massive amount of data. Anandtech had a nice little writeup about SLC vs MLC vs TLC memory a little bit ago:

http://www.anandtech.com/show/6459/samsung-ssd-840-testing-t...

Re: Switch Your Databases To Flash Storage

#22

Post by [deleted] » Mon, Dec 10, 2012, 7:40 PM UTC

buro9 wrote: post #12

I would love if cloud providers offered SSD options for their full range of boxes. For example, to be able to get a Linode at only a fraction more of the cost (say, a 10% premium) with the disk being SSD (and obviously reduced capacity compared to HDD). I have seen the current offerings but found them to either be too costly (AWS, only one of the the largest instances), or too onerous (ssdnodes.com whose base product…

[deleted]

Re: Switch Your Databases To Flash Storage

#23

Post by otakucode » Mon, Dec 10, 2012, 7:42 PM UTC

buro9 wrote: post #12

I would love if cloud providers offered SSD options for their full range of boxes. For example, to be able to get a Linode at only a fraction more of the cost (say, a 10% premium) with the disk being SSD (and obviously reduced capacity compared to HDD). I have seen the current offerings but found them to either be too costly (AWS, only one of the the largest instances), or too onerous (ssdnodes.com whose base product…

Since NAND flash is being price fixed, and likely will be for several more years to come (we're just now starting to see LCD prices drop to reasonable levels after years and years of price fixing, I expect it'll take a similar amount of time for the NAND fixing to get busted and the market to respond), I don't think a 10% premium will be at all possible for a very long time. NAND storage SHOULD be significantly cheaper than rotational storage since it is cheaper to produce, requires fewer exotic materials, has a far wider market, etc. And eventually it will be. But for now, there is a huge premium on NAND storage. I am sure Amazon, EMC, and the others have done the math and simply don't think there is a significant market of people willing to pay for such a service, at least not at the steep rates they would have to charge to meet their growth projections.

Re: Switch Your Databases To Flash Storage

#24

Post by [deleted] » Mon, Dec 10, 2012, 7:42 PM UTC

kyrra wrote: post #21

bunderbunder wrote: post #14

Wear patterns and flash are an issue, although rotational drives fail too. There are several answers. When a flash drive fails, you can still read the data. A clustered database and multiple copies of the data, you gain reliability – a server level of RAID. As drives fail, you replace them. Unlike magnetic disks, SSDs have a tendency to fail at a really predictable rate. So predictably that if you've got two drives o…

I bet you could setup your drives to fail in a set pattern. Lets say you had 4 drives in a RAID-10. If they were all fresh, swap out the first 2 drives when they are at 50% wear... then on you could swap them out back and forth as they approach 100% wear. Since they lifespan of some of the drives (Intel and Samsung I believe) is reported in the SMART data, you could easily do this. SSD drives with SLC memory (enterpr…

[deleted]

Re: Switch Your Databases To Flash Storage

#25

Post by bunderbunder » Mon, Dec 10, 2012, 7:45 PM UTC

venomsnake wrote: post #20

bunderbunder wrote: post #14

Wear patterns and flash are an issue, although rotational drives fail too. There are several answers. When a flash drive fails, you can still read the data. A clustered database and multiple copies of the data, you gain reliability – a server level of RAID. As drives fail, you replace them. Unlike magnetic disks, SSDs have a tendency to fail at a really predictable rate. So predictably that if you've got two drives o…

But with current SSD speed/size ratio this vulnerability window can be only a few minutes, also this can be minimized with mixing batches and vendors of drives.

Hopefully. . . though speaking of speed, there's another pitfall to be aware of: At present, very few RAID controllers support the TRIM command. On one that doesn't any SSDs plugged into it will slow down over time, perhaps becoming slower than magnetic disks.

Re: Switch Your Databases To Flash Storage

#26

Post by eurleif » Mon, Dec 10, 2012, 7:48 PM UTC

[deleted] wrote: post #24

kyrra wrote: post #21

Earlier quoted context omitted.

I bet you could setup your drives to fail in a set pattern. Lets say you had 4 drives in a RAID-10. If they were all fresh, swap out the first 2 drives when they are at 50% wear... then on you could swap them out back and forth as they approach 100% wear. Since they lifespan of some of the drives (Intel and Samsung I believe) is reported in the SMART data, you could easily do this. SSD drives with SLC memory (enterpr…

[deleted]

That's talking about hard drives. The comment you quoted is talking about SSDs.

Re: Switch Your Databases To Flash Storage

#27

Post by debacle » Mon, Dec 10, 2012, 7:49 PM UTC

IheartApplesDix wrote: post #16

pdog wrote: post #15

Earlier quoted context omitted.

Sounds great in theory, but in practice you'll be having that conversation about your database schema anyway.

Nah, just throw it all into a NoSQL store and let the developers figure it out.

The developers will just tell you to virtualize it.

Re: Switch Your Databases To Flash Storage

#28

Post by baruch » Mon, Dec 10, 2012, 7:58 PM UTC

jdcryans wrote: post #9

bcoates wrote: post #6

I love my consumer SSD backed database, but don't get visions of 380,000 IOPS on a real workload quite yet. Like any radical performance increase on just one component it's more likely to just reveal a non-disk latency bottleneck somewhere else in your system. Be aware that the performance characteristics of flash are very unlike spinning disks, and vary widely between models. You will see things like weird stalls, w…

The "weird stalls" can be attributed to GC on lower end SSDs: http://en.wikipedia.org/wiki/Garbage_collection_(SSD)#Garbag...

There are several background operations that happen on ssds, low or high end doesn't matter they all need them. I've seen quite a few supposedly high-end ssds that show abysmal behavior with wide variations in performance across time.

SSD qualification is a tedious job.

It's not even just about performance of the SSD the other points to care about are non-trivial if you intend to use lots of SSDs for important tasks. I collected some questions to consider at http://disksurvey.org/blog/2012/11/26/considerations-when-ch...

Re: Switch Your Databases To Flash Storage

#29

Post by specto » Mon, Dec 10, 2012, 8:01 PM UTC

bunderbunder wrote: post #14

Wear patterns and flash are an issue, although rotational drives fail too. There are several answers. When a flash drive fails, you can still read the data. A clustered database and multiple copies of the data, you gain reliability – a server level of RAID. As drives fail, you replace them. Unlike magnetic disks, SSDs have a tendency to fail at a really predictable rate. So predictably that if you've got two drives o…

Most sysadmins watch counters and set their calendars to replace the drives before they fail since it is so predictable.

Re: Switch Your Databases To Flash Storage

#30

Post by baruch » Mon, Dec 10, 2012, 8:02 PM UTC

bunderbunder wrote: post #14

Wear patterns and flash are an issue, although rotational drives fail too. There are several answers. When a flash drive fails, you can still read the data. A clustered database and multiple copies of the data, you gain reliability – a server level of RAID. As drives fail, you replace them. Unlike magnetic disks, SSDs have a tendency to fail at a really predictable rate. So predictably that if you've got two drives o…

Assuming this predictability is not a good idea in my experience. SSDs fail in various ways, some may be predictable and some are completely unpredictable. It is also not true that an ssd failure means it simply goes to readonly mode. I've seen plenty of SSDs failing unexpectedly and are no longer readable, returning sense key 0x4 (HARDWARE ERROR) and the only recourse is to ship them out.

The risk of correlated failures is indeed non-trivial in SSDs and plain RAID is riskier, be sure to keep a watchful eye on your arrays.