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SSD x 1 + software RAID1 with 2 x 500gb hardware RAID1

Last response: in Storage
November 27, 2012 10:36:46 AM

As the title suggests I am looking into a configuration utilizing a new 256gb SSD as a system drive which can utilize a software RAID1 into an existing 500gb hardware RAID 1 setup. I would be splitting the Hardware RAID1 into 2 partitions. 1 partition to use as the mirror of the SSD and the other partition as extra storage.

The hardware raid is my current system drive but the task I will be undertaking may prove to intensive for the two drives to cope hence the possible use of a SSD. I am revealing data from 5 separate systems with updates of 500kb-2mb ish every second and processing this thro various algorithms before integrating the initial information and processed information into several databases, the system reads and displays this processed and raw data in several real time displays. Also a second pc can read and edit these databases over a gigabit network connection. Average database size is between 1 - 5gb but can exceed 20gb. The main system also sends new updates data over a network connection to a remote server every minute.

Data is very important hence the RAID 1.

My question is, will a software RAID 1 of the SSD work tie-ing it in with a partition on the existing Hardware Mirror ?? Id go check it out myself but id need to go buy the kit and I dont really want to buy the kit if its not going to work. Any suggestions would be helpful. I had also thought about a 4 x 500gb RAID 5 array.

a b G Storage
November 27, 2012 10:50:56 AM

Mirroring an SSD onto a hard drive is probably going to hurt write performance badly. I doubt that it'd be any good for the SSD's read performance either.

Theoretically, if you have a hardware RAID 1 and plan on making a software RAID 1 between the SSD and that lower level RAID 1 array, this should work, but it seems like you're doing a Frankenstein job on the storage, assuming that I didn't misunderstand you.
November 27, 2012 11:27:49 AM

Thanks blazor,

You understood correct. loosing a little SSD performance shouldn't be too much of an issue, i'm fine with that. The only gray area I had was whether I could actually put a software raid on top of the harware raid.

Iv seen in the past through personal experience that an SSD in a software RAID1 mirror with a regular 500gb drive looses maybe 10% overall performance. With the hardware raid below that maybe Ill loose some more performance too but Its still going to be a vast improvement on the current 2 x 500gb setup interms of raw IOPS.

I agree its definitely going to be a bit of a Frankenstein, but It may just work (and also be far less Frankenstein-ish than some other setups iv conjured up in the past).

It would be a far cheaper (and possibly faster) option than a dedicated 4 x 500gb raid 5 mini server or something.

Its a really difficult to explain situation for what I need this setup for, lets just say it involves the use of 2 mass spectrometers, lots of people giving me data, various people wanting to see this live data and finally the security of this very important data...


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a b G Storage
November 27, 2012 12:22:07 PM

You can do all of what you said, but you might benefit from keeping say 20GB of the SSD as a caching partition for the software RAID1 setup or if possible, the hardware RAID1 setup to alleviate the performance impact of RAID with SSD and HDDs.

Also, I'd think that the write impact would be much higher than you said. Your ~10% number seems more like how much the read performance would drop.

What SSD do you intend to get?
November 27, 2012 1:50:25 PM

Yes to the cache partition... that makes good sense to me. thanks for the tip.

Now you come to mention it, the ~10% may well be the read speed only. However, this shouldn't be too much of an issue. It is mainly the read performance that is of importance. Most of the data that the system reads is in full blocks of the databases probably in excess of 1gb at a time when each database section is required. The writes are generally in much smaller size, maybe 5-20mb per update maximum every 30 seconds or so.

I'd probably go for the intel 520 series, but I haven't got that far into the decision making process as of yet. I may look into server class SSDs.

I'm currently setting up the full system in a lab for a full system test. Hopefully by next week I will have generated a fair amount of test data and will have a good idea If my current system will struggle (I'm certain it will, especially with database retrieval and loading times), Once this is proven then it will be time to get a SSD and give it a try.

Thanks for you advice blazor.

a b G Storage
November 27, 2012 2:04:55 PM

Enterprise SSDs are usually incredibly expensive and the majority of them (mostly just excluding some PCIe models) aren't very fast either. You're not writing a lot of data anyway, so most consumer models shouldn't be a problem.

If you want a professional drive, I'd probably recommend a Samsung 840 Pro over Intel 520. It's not the cheapest, but pricing generally isn't too horrible and it is literally the fastest, most power efficient, and probably also the most reliable SSD with a decent price.
November 27, 2012 2:09:09 PM

Excellent, I will bear that in mind. Thanks for the advice. I'll let you know how things progress...

a b G Storage
November 27, 2012 2:09:40 PM

Good luck.
January 3, 2013 1:17:28 PM

hi there, quick follow up. I experimented with some old hardware back home over xmas and in principle it did work. However, i could not simulate the type of writes/reads that would be going on with the software/hardware setup we use in the lab so could not get an idea of real world performance.

Now we're back in the office after xmas/ny we have some new hardware. we went with the ssd and a pair of raid 1 hdd's but with arcornis (i think it was arcornis?) imaging software creating an incremental image update every 30 mins to the raid 1 hdd's. this seems to work well.

In future however the windows storage spaces feature is looking promising, i might try that out if we migrate/upgrade to windows 8.
January 3, 2013 2:04:10 PM

SSD is the best investment. Good luck.
Using SSD and 2TB HD is best then x4 500gb hd