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RAID Boxes

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houkouonchi:

--- Quote from: per on August 04, 2009, 08:42:07 PM ---Hardware raid cards are mostly a total waste if you use ZFS, ZFS does not really use them at all (the only gain is for the write cache. But adding a SLD SSD for the intent log is better, really).

My home-raid can do 650MB/second streaming read, and more than 100MB/second doing 100% random access.
While seeding the 100 or so torrents I'm currently seeding, it's using less than 1% I/O capacity.
Considering the fact that a Gbit network can only handle a little bit more than 100Mb/second, it's sort of good enough. :-)

It contains 15 drives in a 3x5 stripe/raid5 configuration (and a SSD drive for the OS and cache), and is using two rather cheap 8-port PCI-express SATA controllers.

And I really think that ZFS is extremely easy to set up, compared to any of the alternatives, but I have been a unix system administrator since '92.

On a separate note, when you have more than 3 or so drives, you really need to have some kind of redundancy.

If a single drive as a mean time before failure of 5-10 years (which is more or less what I have noticed), you are likely to get a failure per year with 4 drives.

--- End quote ---

100% random access writing and reading what chunk size? There is no way you are can get 650 megabytes/sec with the randomness/small chunks of torrents.

Also what are using to measure io load? iowait is broken on opensolaris. ZFS is all fine and dandy using as a NAS/file-server but it doesn't really work for local storage as I can't run everything I want to using solaris/open solaris so ZFS isn't really an option for me. In that case a hardware raid controller works great and it gives me around 830 megabytes/sec reads and 750 megabytes/sec writes (in raid6) which also happens to be faster than I have ever seen on any ZFS box (especially in writes).

per:
 

--- Quote ---Also what are using to measure io load? iowait is broken on opensolaris. ZFS is all fine and dandy using as a NAS/file-server but it doesn't really work for local storage as I can't run everything I want to using solaris/open solaris so ZFS isn't really an option for me. In that case a hardware raid controller works great and it gives me around 830 megabytes/sec reads and 750 megabytes/sec writes (in raid6) which also happens to be faster than I have ever seen on any ZFS box (especially in writes).

--- End quote ---
Bonnie++ on a 100Gb ZFS filesystem, 4Kb blocksize.

And a 120Gb SSD as cache.

boxer4:
I think I posted this before somewhere but can't find it.

To think of parity and the 'xor' function, here is a very simple case - a 1-bit one: think of a 2-switch 3-way switch light system, like your stairways light where there's a switch on the bottom and on the top.  If you flip one of the switches, the light turns off if it's on, and on if it was off.  Think the light bulb as 'parity'.

Now think of a disk failure as if you cover up a switch or the light bulb (NOT if the light bulb burns out).  (Depending on how your house was wired or switch was installed, the explanation can vary...) Because of the unique property that each switch will change the status of the light bulb, if you knew how your house was assembled, given that you knew the position of one of the two switches (up or down) and whether the light was on or off, you can deduce the position of the other switch -- unambiguously.  Same if the light bulb - if you knew the position of the two switches, you can tell whether the light should be on or off.

for this example house, say

Switch1....Switch 2...Lamp
down....down....off
down....up......on
up....down......on
up......up......off

There is no other possible 'legal' states this system can be in... like down-down-ON is impossible (the light spontaneously turned on for no reason???)

Because you know whether the unknown switch is on or off, or if the unknown light was on or off, you can now replace that bit-piece of information, and that's basically how data is recovered from RAID.

If you code up your disk to billions of little switches and light bulbs, 8 per byte, you can see how you can recover the data if you lose a disk.

I run software RAID5 (Linux-MD) on my home machine with 4 disks.  Still trying to switch over from my 4x120G disk array to my 4x500G hot swappable array...  (That day will come when WoW is stable in Linux, I suppose...)

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