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05-01-2011, 07:51 PM #1Aspiring Evangelist
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Best way to use an SSD in a server/virtualized platform with regular drives?
I'm thinking Linux and Xenserver in general. And also I'm thinking of SSD for the databases.
So the regular drives are in an array which you use to create the VMs on. The SSD would be in its own storage.
After you're done creating the VM, you add in a new drive using the ssd storage then you mount it on /var/lib/mysql in linux.
Would that be the best way to do this? Anyone have a different opinion on the best method to take advantage of an SSD in a preexisting environment?
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05-01-2011, 07:53 PM #2Web Hosting Master
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Sounds like a good idea to me, only thing I'd be way about is redundancy.
Sure SSD's are fast, but they dont like lots of tiny write cycles.
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05-01-2011, 08:01 PM #3Aspiring Evangelist
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Can you actually raid them? at least a mirror raid. From what I read, there aren't any raid cards that can do it yet. I'm considering getting like 2 64gig ssd for this idea. If I can't raid them, I suppose I would need a backup very often
Also I wonder about performances under the Virtualized environment. I assume it would be similar to a regular raid array.
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05-01-2011, 08:07 PM #4Web Hosting Master
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I saw a YouTube video where they put 24 SSD's in RAID0 for a test. So I do think it is possible:
http://www.youtube.com/watch?v=96dWOEa4Djs█ Tailored VPS offers fully customizable VPS Hosting
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05-01-2011, 08:18 PM #5Aspiring Evangelist
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Yea I've seen that too but I'm not exactly sure about that. From what I read, raid cards right now don't support TRIM.
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05-01-2011, 08:20 PM #6Web Hosting Master
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05-01-2011, 08:21 PM #7Web Hosting Master
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Linux software raid-1 would do the job, you can keep AHCI then for TRIM.
Linux software raid has barely any overheads vs a hardware controller, you can always allocate 1 core of your CPU to the host machine and the rest for VPS, to ensure its consistently performing.
@Visbits - I'm with the times thanks, I build + repair high end systems for a living. I'm not denying SSDs are great for database applications, but the fact remains that most SSDs do not take lots of tiny write cycles well and leads to a short lifespan in comparison to a mechanical HDD. It varies a lot depending on which SSDs you use..
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05-01-2011, 08:48 PM #8Web Hosting Master
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If your employing any thing but SLC for write applications at all your a fool. The fact any one would consider an MLC drive baffles me, if its intense stack tons of 15k together or pay for SLC. IO Drive are fairly well priced now days..
The write life of modern SLC is some high PB number... I think 2.4PB for an 32GB X25-E...?? A mechanical disk would take years to even hit that.'Ripcord'ing is the only way!
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05-01-2011, 10:17 PM #9Aspiring Evangelist
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Any specific ones you guys recommend?
I was looking at the OWC http://eshop.macsales.com/search/MX040Select
I don't need that much space as the DBs are not that big. I know these are SLC but there are probably better ones. Pricing isn't so bad at all.
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05-02-2011, 02:47 AM #10
I do exactly what you're suggesting without any issue. The only problem really is the extra cost, which most people don't want to pay, and the small size of the drives.
We're using the Intel X25-E, but if I could do it all over again, I would use the Intel X25-M (or the newer 320 series) in order to get more space at a lower cost, as those versions still perform fine and cost a lot less.IOFLOOD.com -- We Love Servers
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05-02-2011, 04:15 AM #11Aspiring Evangelist
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funkywizard,
aren't those non-SLC ssd?
How do you deal with backups? do you use a simple mirror raid then? Any issues with that?
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05-02-2011, 10:25 AM #12
Yes, the X25-M and 320 series are not SLC. They work fine. We have been using the SLC based X25-E, but that's been overkill.
Yes, we use raid 1. Backups are our customers responsibilities. Since we run Xen, we can't just back up the entire server using one r1soft license, so we leave it up to the customer what kind of backups they want to use as the cost of the backups alone can easily be as much as the entire vps.IOFLOOD.com -- We Love Servers
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05-02-2011, 12:10 PM #13Web Hosting Evangelist
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Also you could look into two emerging technologies.
The first is Adaptec's Hybrid RAID where it uses SSDs for read and SAS/SATA for writing. This provides a great deal of increased performance but without the nasty effect of too many writes on the SSD drives (it essentially uses the SSDs as cache).
The second is LSI's Cachecade (which is available on the Dell H700) which is also a Hybrid SSD/SAS/SATA raid combo.
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05-02-2011, 12:58 PM #14Aspiring Evangelist
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funkywizard,
How do you sell that? Do you have a charge say like you can buy 10 gig of ssd mysql space? Then you add it exactly how I described it? Do you just use onboard sata ports for that or are you using a raid card (so you can hot swap the ssd too).
XLHost, thanks.. but they sound expensive lol.
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05-02-2011, 02:14 PM #15
The effect here is the opposite of what you'd expect. First of all, the read cache isn't particularly effective. If you look at benchmarks for this hybrid drive, the results are not that impressive. Secondly, it's wrong to assume that just because it's being used to cache reads, that there will be no writing. In order for a cache to be effective, it needs to be filled with whatever data the caching algorithm thinks will be read. LRU is the most common algorithm for this, and it tends to lead to a lot of writing as the cache is continually updated. Caches are actually some of the most write heavy applications you can come up with.
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05-02-2011, 02:17 PM #16
First off you don't need a raid card to use hot swap.
Secondly, yes, onboard sata ports, s/w raid 1. And yes, we allow people to buy 2 or 4gb of SSD space, and unless they ask otherwise, with 2gb SSD, 500mb will be mounted as swap, and 1.5gb as /var/lib/mysql, with 4gb, the default is 1gb for swap and 3gb for /var/lib/mysql.
A few people are using it and like it a lot, but for the most part people would rather save their money. If I were using the 320 series instead of the X25-E, then I could get something like 5x the space for the same money, and could even consider putting all of someone's disk usage on SSD instead of just mysql / swap.IOFLOOD.com -- We Love Servers
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05-02-2011, 02:49 PM #17The Guru!
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If you want fast read speed, why don't you try SAS Raid array + MaxIQ?
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05-02-2011, 05:31 PM #18Web Hosting Guru
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Your statement might have been correct 3 years ago. But today even enterprise drives use MLC.
FusionIO, the super high end enterprise PCI-e SSD company, uses MLC.
The next generation of Intel X25-E coming out later this year will also be using MLC instead of SLC.
In this day there's no reason not to use MLC.
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05-02-2011, 05:48 PM #19Web Hosting Guru
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Actually all the OWC Mercury Pro drives you mentioned are MLC, not SLC.
In reality in this day the last thing you need to worry about is MLC vs. SLC. MLC is very good and plenty of enterprise drives such as FusionIO use MLC.
For database use what you REALLY need to worry about is durability. Did you know that most SSD use a write cache that will lead to data loss or corruption in a power outage? Yup that includes SLC drives like Intel X25-E. You WILL lose data or get corrupted data in a power loss.
To avoid that problem you need a SSD with supercapacitor that will flush data from cache into storage in a power loss.
I know of 2 mainstream SSD that offers supercapacitor:
1) OCZ Vertex 2 Pro -- http://www.ocztechnology.com/ocz-ver...i-2-5-ssd.html (the next gen Vertex 3 pro is coming out any day now)
2) Intel 320 -- http://www.intel.com/design/flash/na...s/overview.htm
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05-02-2011, 06:09 PM #20Web Hosting Master
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05-02-2011, 06:20 PM #21Web Hosting Guru
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05-03-2011, 02:25 AM #22Aspiring Evangelist
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Thank you for all the responses. This is a great thread!
I learned a few new things such as using ssd for swap. That didn't even came in my thought. I don't need anymore then 40 gigs as my datbases generally are medium size forums/blogs. So I think 2 of these wouldn't be so bad http://www.newegg.com/Product/Produc...el+320&x=0&y=0
only 100 dollars each. Definitely doable and cost effective.
Although the writes seems to be slower for these but I suppose thats ok as most of the forum is in reading anyway.
Thanks guys.
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05-03-2011, 02:44 AM #23IOFLOOD.com -- We Love Servers
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05-03-2011, 10:29 AM #24Aspiring Evangelist
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Thanks. I see what you mean by the 80 gig. Still affordable. I'll wait for a good deal to come up and get 2.
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