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RAID 1 On A Web/Database Server: Software or Hardware

post #1 of 33
Thread Starter 
I've recently had a conversation with an admin of a pretty popular website. He's of the opinion that software RAID 1 on Linux is crap and that hardware RAID 1 is better (at least for their purposes). The website has just over 200,000 users and runs the usual LAMP stack as well as the gazelle CMS and the Ocelot tracker.

The box it's running on sees a few hundred gigabytes of writes per day, and seemingly RAID 1 couldn't keep up in terms of I/Os, so they split the I/O tasks between two independent SATA drives rather than RAIDing them.

Would a hardware-based RAID 1 really make that much difference? If so, how?
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post #2 of 33
A hardware RAID system is faster as it has a dedicated CPU for RAID algorithm and higher end cards have dedicated memory for caching and access speeds (as well as handling the algorithms)

If you want an inexpensive but high end RAID card, go with the PERC 6 (they are inexpensive on ebay) and get SAS to SATA adapters.

You should also be using RAID 5 as it offers parity as well as faster I/O.
Edited by appleg33k85 - 2/15/13 at 9:10am
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post #3 of 33
Thread Starter 
Quote:
A hardware RAID system is faster as it has a dedicated CPU for RAID algorithm and higher end cards have dedicated memory for caching and access speeds (as well as handling the algorithms)

Which is exactly the point of my post. RAID 1 does NOT involve any calculations at all, therefore there are no algorithms to implement.
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post #4 of 33
It still takes CPU cycles, its not going to be a huge gain in performance but there will be one. Though again, RAID1 isn't good for quite a few people accessing a server thumb.gif
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post #5 of 33
Thread Starter 
@appleg33k85

This is what I thought. I don't understand why he was blaming software RAID when he was using a RAID 1 pair to serve that many users. Apart from local caching, a system based around a hardware RAID card would still struggle in that configuration, with that many users.
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post #6 of 33
He should be using RAID 10, IMO. Better IOPS.
With a hardware RAID controller, writes will go to cache first which will report back that the write was successful faster then later write to the drives when necessary.
post #7 of 33
Thread Starter 
@tycoonbob

I agree about using RAID 10, I don't think RAID 1 is good for a write-heavy database.

On a box with loads of RAM, will a hardware controller in RAID 1 be much more performant than software RAID on the same hardware, due to the localised caching of the RAID controller?
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post #8 of 33

software/hardware is (almost certainly) irrelevant here - the problem was using RAID1 at all.  The IOPS boost over a single drive is minimal, compared with having 2 independent drives which will almost double their performance for this task.

 

Really they should look at a pair of SSDs in RAID1 (software or hardware, it won't matter) - many controllers will give you RAID0-like sequential speeds from a RAID1 array of SSDs, with more IOPS than you can shake a stick at...

post #9 of 33
Thread Starter 
@the_beast

Greetings! I haven't seen you for an age! Keeping well, I trust? biggrin.gif

You're right about using RAID 1, I think this was on a temporary server while they upgraded the original but still, RAID 1 would not have been my choice. They've looked at enterprise SSDs (they're seeing 800GB in database writes per day) but those are kind of pricey, so I think it'll be 10K SATA or 15K SAS in RAID 10.
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post #10 of 33

Been a while - house project meant little time (and no real net access) for the last year, and a baby due in the next few weeks isn't going to help.  I'm not on OCN so much nowadays.

 

I'd still go for a RAID1 with consumer SSDs to be honest, coupled with some healthy caching and allowing the cache to remain dirty for a little longer than normal to protect them from too many writes.  The super cheap prices we're seeing now mean I'd be more than happy to have a few drives fail on me (though I haven't actually seen any drives fail yet due to write cycles, all the failures I've seen appear to have been controller issues) and swap them out rather than pay the very high cost for the limited extra performance you'd get from 15k drives - they really aren't that much faster than bog standard SATA in the grand scheme of things.  They may give you double or even quadruple the IOPS, but when compared to an SSD they're still pitiful, especially when price is taken into consideration.

 

The other thing I'd look at would be some kind of RAM caching/RAM disk-type application - if the database is small enough that is.  I'd need to know the server is properly dual-corded (if in a DC) and UPS backed (if SOHO - if your DC ain't UPS backed then move!).

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