RAID 0 vs RAID 5

[ratdude747]

Re: RAID 0 vs RAID 5

I forgot to upgrade the firmware and under load she croaked...

A firmware reload later... since I have to redo it anyway (I have a bad feelign there was some corruption involved)... I recreated the array using 256kb stripes (just to see if there is a performance difference).

[ratdude747]

Re: RAID 0 vs RAID 5

Updates!

1. The card's bios let me test the battery... it returned an estimate of 255Hrs.

2. The drives came today... I ended up RAID 0'ing them and using a 4kb stripe size; I read that when commands aren't in queue, then smaller sizes are better. Correct?

[dood]

Re: RAID 0 vs RAID 5

^
Good score, just hope the batt is good. There's a web based config and maintenance utility under windows which will fully test and charge the battery for you. Not sure how this is supported under linux.....but regardless, good deal!!

Just to add some more information to the thread... On many enterprise RAID controllers, if you don't have the battery installed, they won't even let you enable write caching.

Also, in my last batch of HP servers, I ordered them with a flash-backed cache card instead of battery-backed. I was surprised to find that they still had a plug-in module for the cache card, until I realized that it was just a small capacitor bank to take place of the battery.

Also, with the HP servers, if you don't install a cache module at all, your RAID options are 0, 1, and 5. You can only run 10 if you have the module installed. Of course, even if you're running 0, 1, or 5 anyway, the speed increase by adding a cache module is quite dramatic.

[eccerr0r]

Re: RAID 0 vs RAID 5

I have two software 4-disk "self booting" RAID5s and luckily I haven't had too many corrupted data yet. I usually run the whole server machine on a UPS to help against the write hole (which though is an issue I'm not terribly worried about as parity is written last). Performance is nowhere near theoretical peak but is acceptable. I run 4-disk because when I set it up, I was kind of appalled at the "waste" disk space the redundancy needed but it's not an issue anymore. I run the RAID mostly for uptime in case a disk buys the farm I can still access the machine from the net. I haven't had too many disk failures lately, but when a disk did go down, my machine stayed up...

One of my raid5's is in a 4-in-3 hotswap bay. Knowing which disk is which during a hotswap is scary, have to basically hammer the disks with activity and the bay with the dead LED contains the dead disk...

[ratdude747]

Re: RAID 0 vs RAID 5

He has 4, which is enough.

But the case can only hold 3. my PSU also only has 3 SATA connectors; the only modular cables included were a Molex strand, a Molex/berg (floppy) strand, and a SATA strand. Actually, its a perfect fit for the case and drive layout.

Technically I could start using 5.25" adapters in the lower 2 optical bays... but due to cooling issues (not much clearance with the HOT ram nearby), it ain't happening... I hate those adapters.

[shovenose]

Re: RAID 0 vs RAID 5

He has 4, which is enough.

[Uranium-235]

Re: RAID 0 vs RAID 5

yeah if it can do raid 10, i'd say go that route, though it requires more drives

[shovenose]

Re: RAID 0 vs RAID 5

I have never like RAID5. wish your case could do 4 drives then you could put the 4 Raptors in RAID10 I love 10.

[ratdude747]

Re: RAID 0 vs RAID 5

^
Good score, just hope the batt is good. There's a web based config and maintenance utility under windows which will fully test and charge the battery for you. Not sure how this is supported under linux.....but regardless, good deal!!

And if it isn't, well, I can get chinese replacements for $10 a pop... I know, china batts suck, but good luck finding an OEM one that isn't as worn.

[Topcat]

Re: RAID 0 vs RAID 5

^
Good score, just hope the batt is good. There's a web based config and maintenance utility under windows which will fully test and charge the battery for you. Not sure how this is supported under linux.....but regardless, good deal!!

[ratdude747]

Re: RAID 0 vs RAID 5

Never mind... Problem solved:

http://www.ebay.com/itm/321049006379

Snared one for $30 shipped... w/o cables (as per my offer that was accepted).

Same card, only the 12 port version.

In the worst case, if the BBU happens to be roasted, I can get aftermarket bare batteries for $10...

Besides, the HDD LED connector on my 4 port was in sad shape... I had hacked it (see the thread linked in the first post) but it never wanted to stay connected...

Win?

[ratdude747]

Re: RAID 0 vs RAID 5

Well then screw me with an iron pipe... I get to pick between a jack and a bbu.

If I had known this I wouldn't have have bought the drives... too late now. If they had only made the bbu standard equipment...

[Topcat]

Re: RAID 0 vs RAID 5

I thought the bbu was only for RAID 5.

Last I checked the 9500s bbu was ebaying for $80ish.

No, it stores any data that was in the controller cache in the event of a crash or power loss, and at the next POST it writes this data back to the place it needs to be.....hence preventing dataloss. Worth every penny, if you've ever had dataloss or corruption, you'll understand!! It comes into play anytime you have write caching enabled. If its disabled, the BBU is of no use. The RAID config is of no importance when it comes to write caching.

[ratdude747]

Re: RAID 0 vs RAID 5

RAID1 or JBoD until you get the BBU. The 3ware controller is useless without it, take it from me...I've had a lot of experience with RAID's. If you have write caching enabled and it crashes or you lose power, kiss data goodbye. Its safe without the BBU if write caching is disabled, but what's the point, it seriously hinders performance. With the BBU and good drives, and its not mission-critical data, raid0 all the way! it will be smokin' fast!

I thought the bbu was only for RAID 5.

Last I checked the 9500s bbu was ebaying for $80ish.

[smason]

Re: RAID 0 vs RAID 5

With RAID 0, lose any drive, lose everything, so RAID 5 would be my choice given the current options.
I literally just got back to my desk from replacing a failed drive in a RAID 10 iSCSI SAN. I love being able to replace a failed drive with no-one ever knowing there was a problem.

[Topcat]

Re: RAID 0 vs RAID 5

RAID1 or JBoD until you get the BBU. The 3ware controller is useless without it, take it from me...I've had a lot of experience with RAID's. If you have write caching enabled and it crashes or you lose power, kiss data goodbye. Its safe without the BBU if write caching is disabled, but what's the point, it seriously hinders performance. With the BBU and good drives, and its not mission-critical data, raid0 all the way! it will be smokin' fast!

[ratdude747]

Re: RAID 0 vs RAID 5

Eh if it's not going to be a storage server, go for raid 0. Do the raid 0 on the controller if you're going to use it as the root partition. You can do the same on raid-5 and get redundancy, but it will write moderately and read fast, it's good for systems that needs to be up 24/7, still suffers the write-hole.

My thoughts exactly. This array will be the only hdd's in the sytem and thus, it will have root.

[Mad_Professor]

Re: RAID 0 vs RAID 5

It really comes down to your own needs.
Some call RAID-5 "destructive"
That is because it does not store data sequentially on the media, it is chopped up in pieces and spread out over how many disks you have.

SSD's from some manufacturers work in similar fashions, data is compressed etc before stored to flash.

The downside is when you need to do data recovery it becomes more complex, but as it is there exists good tools for rebuilding broken RAID-5 arrays with missing harddrives (RAID Reconstructor is my personal favorite)
But for sure, RAID-1 is allot simpler, just throw away the broken drive or controller and your data is still there on the remaining disk with no problem.

Of course single disk failure in a RAID-5 is no problem aswell, controller failure is another thing. Then you either need software like my recommendation above or a new compatible RAID card...

I personally run RAID-5 with 3x 1TB drives but in hindsight I would have gone with RAID-1 or RAID-10 instead and a cheaper RAID controller.
You are on the right path though, the reason I went hardware RAID was due to very bad experience with Intel's onboard ICHxR RAID controllers sold on mainboards with Intel Chipsets

I think it is pointless to compare RAID-0 with the others, because it is not even "RAID = Redundant Array of Independent Disks" at all, it is a single point of failure thing.

That's why I went with the software route, like mdadm and zfs. You can still recover it on other machines without being crippled to proprietary hardware or algorithms. I wouldn't do the fake-raid cards though, I've been burned on that, highpoint, and simple cheap controllers from promise and syba, learned my lesson there.

The drives are 74GB a pop.

I do have 8gb Of ECC ram in the system... but I'm not gonna ZFS. Why do that when I have a Hardware RAID card already (it has 128mb of ECC SDRAM onboard).

These are the three drives to my main rig, which runs on Debian (or perhaps a different i686PAE distro). Everything will be on the array, with 3 partitions ("/", "/boot", swap).

There won't be any mission critical data on the system... anything important gets backed up on my fileserver.

----

Still leaning towards RAID 0 because of the speed boost...

Because ZFS can catch and fix silent data corruption and unrecoverable errors, checksumming of all disks and ensures that all data is flushed to disk and not sitting in cache along with journaling, not to mention triple parity and snapshot abilities. But still, this relies on quality hardware not being faulty.

Hardware raid would be oblivious to this, and of course with the raid-5 write-hole you would need a BBU to ensure the array is written out, and you still have to rely on filesystem for error checking and correction, and even though it may appear ok, you could get an Unrecoverable Read Error (URE) on any of those disks or silent data corruption and so on, but the chances of that happening are seldom.

Anyways...

Eh if it's not going to be a storage server, go for raid 0. Do the raid 0 on the controller if you're going to use it as the root partition. You can do the same on raid-5 and get redundancy, but it will write moderately and read fast, it's good for systems that needs to be up 24/7, still suffers the write-hole.

[ratdude747]

Re: RAID 0 vs RAID 5

It depends on what you're going to use it for.

How big are the new drives?

Raid-5 is good for smaller drives, but if over 1TB, you're asking for trouble, I was lucky running 6 1TB in raid 5 for 3 years, before 6 months ago I moved to ZFS.

why not just jbod, and get ZFS. It comes on bsd distros, zfs on linux, zfs fuse, opensolaris, openindiana.

You can do raidz or z2, and have guarantee data integrity with zfs, if that's important to you. Only downside is you need a lot of ECC ram.

It really depends on what you're going to do with them.

The drives are 74GB a pop.

I do have 8gb Of ECC ram in the system... but I'm not gonna ZFS. Why do that when I have a Hardware RAID card already (it has 128mb of ECC SDRAM onboard).

These are the three drives to my main rig, which runs on Debian (or perhaps a different i686PAE distro). Everything will be on the array, with 3 partitions ("/", "/boot", swap).

There won't be any mission critical data on the system... anything important gets backed up on my fileserver.

----

Still leaning towards RAID 0 because of the speed boost...

[Per Hansson]

Re: RAID 0 vs RAID 5

It really comes down to your own needs.
Some call RAID-5 "destructive"
That is because it does not store data sequentially on the media, it is chopped up in pieces and spread out over how many disks you have.

SSD's from some manufacturers work in similar fashions, data is compressed etc before stored to flash.

The downside is when you need to do data recovery it becomes more complex, but as it is there exists good tools for rebuilding broken RAID-5 arrays with missing harddrives (RAID Reconstructor is my personal favorite)
But for sure, RAID-1 is allot simpler, just throw away the broken drive or controller and your data is still there on the remaining disk with no problem.

Of course single disk failure in a RAID-5 is no problem aswell, controller failure is another thing. Then you either need software like my recommendation above or a new compatible RAID card...

I personally run RAID-5 with 3x 1TB drives but in hindsight I would have gone with RAID-1 or RAID-10 instead and a cheaper RAID controller.
You are on the right path though, the reason I went hardware RAID was due to very bad experience with Intel's onboard ICHxR RAID controllers sold on mainboards with Intel Chipsets

I think it is pointless to compare RAID-0 with the others, because it is not even "RAID = Redundant Array of Independent Disks" at all, it is a single point of failure thing.