siadam Posted January 12, 2011 Posted January 12, 2011 From what little I've seen, people are saying 10 > 5? Is this true?
featured_spectre Posted January 12, 2011 Posted January 12, 2011 depends on what you want... If you want speed RAID 5 If you want redundancy RAID 10 (not 01 as that can cause issues) RAID 6 is also making its way in, but I haven't tested so cannot comment
Soulfish Posted January 12, 2011 Posted January 12, 2011 Raid 10 is faster than Raid 5, however Raid 5 gives greater capacity for the same number of disks. For most general workloads utilising a modern controller with a decent cache size and good RAID algorithm implementation RAID 5 is (now) pretty similar to RAID 10, until you start hitting large numbers of random writes. For that reason I'd normally go for RAID 5 (or 6 which is just 5 with an extra parity drive) unless you needed the performance, or could afford to run RAID 10. For our latest SAN we run a mixture of RAID 1, RAID 10 and RAID 6 depending on the storage tier. For tier 0 (SSDs) we run in RAID 1 since they're already pretty fast and we need the redundancy, for tier 1 (15k SAS drives) we run in RAID 10 to get the best performance, and for tier 2 (7.2k SATA disks) we have one pool of RAID 10 for apps that need a bit more performance, but aren't quite important enough to make the higher tiers or for high speed file stores and one pool of RAID 6 for general purpose file stores.
Butuz Posted January 13, 2011 Posted January 13, 2011 Using Raid-TP on my Sun 7110's (Disk Striping with Triple Distributed Parity). This provides the ultimate combination of reliability, quick rebuilds and performance. You do however sacrifice 75% of your capacity at this raid level. That is not an issue currently for us. It may be an issue in the medium term though in which case I will have to move back to Raid 6 to reclaim some more free space. Will cross that bridge when we come to it! Butuz
synaesthesia Posted January 13, 2011 Posted January 13, 2011 I will shoot people on sight using Raid10, it's just daft and a waste of resource. Raid 5 with a hotspare is certainly a much better bet out of those two.
featured_spectre Posted January 13, 2011 Posted January 13, 2011 synaesthesia...why do you say that? RAID5 drive failure can mean alot of files lost, but with RAID10 the files can be saved...however each to their own!
kmount Posted January 13, 2011 Posted January 13, 2011 synaesthesia...why do you say that? RAID5 drive failure can mean alot of files lost, but with RAID10 the files can be saved...however each to their own! He had a fight with a RAID10 box recently. *hides*
siadam Posted January 13, 2011 Author Posted January 13, 2011 Great info here guys, appreciate the help. I was leaning towards 5 anyway, used it in the past and it seems this has confirmed my confidence. Thanks.
Butuz Posted January 14, 2011 Posted January 14, 2011 I will shoot people on sight using Raid10, it's just daft and a waste of resource. Raid 5 with a hotspare is certainly a much better bet out of those two. Disagree with that! Raid 10 has it's place. The only Raid anyone can definitively be shot for using is Raid 0 and infact I think shooting would be too easy for a Raid 0 user – hung drawn and quatered would be more appropriate!!! Bear in mind Raid 5 has great read performance but poor write performance so be careful on how you use it. Good for a file server that has lots of data read from it, bad for a database server that has lots of heavy writes. Butuz
tonyd Posted January 14, 2011 Posted January 14, 2011 Hmm, not sure in what way RAID 0 (AKA Suicide RAID) can be called RAID anyway - definitely no redundancy there.
sted Posted January 14, 2011 Posted January 14, 2011 Disagree with that! Raid 10 has it's place. The only Raid anyone can definitively be shot for using is Raid 0 and infact I think shooting would be too easy for a Raid 0 user – hung drawn and quatered would be more appropriate!!! Bear in mind Raid 5 has great read performance but poor write performance so be careful on how you use it. Good for a file server that has lots of data read from it, bad for a database server that has lots of heavy writes. Butuz raid 0 does have uses. My home nas box is striped to give me 4tb of backup space but its is just backup so if that goes i replace the drive(s) and copy the data back
Butuz Posted January 14, 2011 Posted January 14, 2011 Yeh I guess it's useful if you want an unreliable backup nas box! Butuz
sted Posted January 14, 2011 Posted January 14, 2011 Yeh I guess it's useful if you want an unreliable backup nas box! Butuz but it is a backup whats the likelyhood of that my pc and my laptop all losing the data at the same time?
synaesthesia Posted January 14, 2011 Posted January 14, 2011 That Raid10 fight is still ongoing (although now it's nothing to do with the RAID, it's just further incompetence from my now ex employer). Also it's rather better on a decent raid controller than it is on an entry level HP server with onboard fakeraid which does *not* allow on the fly builds >:| So, apologies for the previous shout which was slightly tainted by my altercation (nurses a black eye and split lip)
Popular Post mister_z Posted January 16, 2011 Popular Post Posted January 16, 2011 Descending into geekdom with a senior IT guy. My teams manage storage, and I architect storage solutions for various projects, so be warned. . . Mr. Z's First rule: RAID IS NO SUBSTITUTE FOR FULL AND TESTED BACKUPS. Now, for those who don't want to read further: Chances are excellent that RAID 5 will fill the bill for most educational projects. Short form: It's highly redundant, and the only performance penalty is during write activities. BE CERTAIN you can detect failures and address them promptly, have spares, and you should be fine until the equipment ages. Longer form: RAID 5: Uses a number of disks (typically 3 to 8) to create a "RAID Group." Visualize an 8-layer cake. Instead of a sector on one disk, like a slice of one layer, there is a "stripe," a slice cut thru all the layers. In that stripe, 7 of the pieces contain data, the 8th contains parity information. If you lose one "layer," the information for all the stripes can be recreated as long as all pieces of all 7 other layers remain intact. The parity sector is calculated during a write operation, and is written in round-robin fashion to layer 1 for the first stripe, layer 2 of the next stripe, etc. Disadvantage ? These parity calculations take time and processing power, which is why I do not specify this RAID level for highly "write-intensive" applications like a transactional database with 3,000 concurrent users. But I doubt this is a serious issue in most educational uses. Advantage ? Saves money -- you only need one disk worth of overhead to carry the parity information. But don't get carried away. . . One thing to watch for -- as I mentioned already -- is to be certain you can detect failures promptly. When (NOT "if") a disk fails, you need to discover that and to replace it promptly. The system will typically begin reading every sector of every other disk (called running in 'degraded mode') to recreate the missing data both for user operations and to rebuild the disk when you replace it. IF A SECOND DISK FAULTS BEFORE THE REBUILD COMPLETES THE RG IS TOAST. That's why you replace failed disks promptly, and never put "too many" disks into one RG. I have been consulted after people build RAID 5 RGs with 15 disks, and 4 years later two fail. They ask "what can we do ?" and I tell them to reach for backups. (See my first rule) So, as disks get larger, the rebuild times takes longer. Which leads to . . . RAID 6: Like RAID 5, but the parity information is written to 2 disks in the RG. Advantage: Lose 1 disks and there is no degraded mode operation per say. Lose a second disk during rebuild and then the system shifts to degraded mode. BUT, it's not a disaster. Disadvantage: Higher cost ("wastes" another disk over RAID 5), not all controllers support RAID 6 yet. Also resistant to LSE's Latent Sector Error (LSE) - When a disk has a weak sector but either that data has not been read from, or the system corrected for it. You find in on a RAID 5 system when a DIFFERENT disk fails, and you try to rebuild. The system tries to read the weak sector, and OOPS!" Which is why RAID 5 on aging systems can be problematic. Sophisticated enterprise-class storage from EMC or Hitachi performs "disk-scrubbing" in the back-ground, constantly looking for weak sectors and moving the data. But lower-end systems typically do not have that option. If your controller supports it, make sure it's turned on. Lastly, for the performance geeks out there: RAID 0 - Not redundant at all. Writes data across multiple disks, which gives a very high I/O capability, but does not calculate nor does it write any parity information. Good for very little in the business setting, since downtime will occur eventually. RAID 1 - Mirrors 2 disks. No parity information to calculate, so in general as fast as a single disk, but with redundancy. But doubles the disk costs. Used as higher write performer than RAID 5 / 6. Composite RAID: RAID 1 + 0 or RAID 10 - Mirror multiple pairs of disks to create RGs, then stripe across those RAID 1 RGs to create a RAID 0 super-RG. Redundant due to mirroring of individual pairs, very fast, since there are no parity calculations, and with great potential due to the available I/O bandwidth. Quite safe: A complete failure requires BOTH halves of any one mirrored pair to fail. RAID 0 + 1 - Stripe then mirror. Don't do it. Unlike RAID 10, if you lose just ONE disk in each RAID 0 RG, you're toast. RAID 5 + 0 / 50 - composite multiple RAID 5 RGs then stripe across them. Improved performance over RAID 5. Lastly, for people using RAID, CREATE A HOTSPARE. This is a mechanism for the system to keep one disk aside for emergencies. If a running disk fails, the system will "swap in" the hot spare and begin the rebuild. It reduces the vulnerable time MONITOR THE SYSTEM. It sucks to have the system swap in the hot spare and for you to not know it, Hope that answered your questions. 6
ChrisH Posted January 16, 2011 Posted January 16, 2011 (edited) Thanks that's very comprehensive. I currently have RAID 6 on my HP SAN and it does indeed run the scrubber utility and there is a hot spare available. The SAN also sends plenty of emails too many sometimes Edited January 16, 2011 by ChrisH
Hebdenlad Posted January 17, 2011 Posted January 17, 2011 Morning all. So.... what you really need is data integrity (i.e. knowing that when you write a block of data to your filesystem you are safe in the knowledge that you can read it back at any point in the future). There is only one filesystem that can guarantee this.... ZFS (and to save me writing shed loads look here: ZFS - Wikipedia, the free encyclopedia). Any form of RAID only gives you protection against disk failure and allows you to carry on (albeit at a reduced performance rate) whilst the parity is rebuilt on the hot spare. With ZFS the parity is only rebuilt on the blocks that are used. So for example, if you have a RAID set made up of 2TB drives (not uncommon nowadays) with 100GB of used capacity and you have a situation where one fails and the hot spare kicks in you only rebuilds the parity on the 200GB and NOT the whole drive like other filesystems will force you to do. This means your "slow down" is considerable less. Regarding the read and write performance issues noted above, ZFS is the only "SSD aware" filesystem. What that means is ZFS understands about SSDs and uses them intelligently for both reads and writes to drive greater performance thus alleviating the need for "tiers of storage" and the associated management overhead maintaining data in the correct tier. I am more than happy to explain this in detail off forum if anyone wants to know more. Regards, Phil 1
SYNACK Posted January 17, 2011 Posted January 17, 2011 What systems now support zfs as it kind of got muddy after Oracle brought Sun?
Hebdenlad Posted January 17, 2011 Posted January 17, 2011 What systems now support zfs as it kind of got muddy after Oracle brought Sun? Hi there, So the systems that support ZFS are the S7x20 range (Sun Unified Storage | Flash Optimized Storage | Oracle). These use the latest Intel Nehelam and Westmere CPUs and support read and write SSDs (model dependant). If you need more information then drop me a line and I can put you in touch with your local Oracle storage sales person Regards, Phil
SYNACK Posted January 17, 2011 Posted January 17, 2011 If you need more information then drop me a line and I can put you in touch with your local Oracle storage sales person the last time I checked into Sun gear it took two weeks to find out that they apparently did not consider NZ a worthwhile market and everything would have to be imported from Australia at horrific prices (more than double UK pricing). I would be interested if this has changed any though so that I could give Sun/Oracle products another shot in the future.
Hebdenlad Posted January 17, 2011 Posted January 17, 2011 the last time I checked into Sun gear it took two weeks to find out that they apparently did not consider NZ a worthwhile market and everything would have to be imported from Australia at horrific prices (more than double UK pricing). I would be interested if this has changed any though so that I could give Sun/Oracle products another shot in the future. Hi, not sure about this... Let me see if I canget hold of my Australian opposite number... 1
dhicks Posted January 17, 2011 Posted January 17, 2011 the systems that support ZFS are the S7x20 range Does ZFS need special (i.e. Sun-only) hardware support to work correctly / with realistic performance? I tried using ZFS on a Linux system running on commodity hardware but got corrupted files - is this likly to have been the Linux implementation of ZFS, the hardware not being up to the job in some way, or something else? -- David Hicks
dhicks Posted January 17, 2011 Posted January 17, 2011 My teams manage storage, and I architect storage solutions for various projects While we have a RAID expert here... We've just bought a QNAP storage device - a 2U server with 8 hot-swap SATA drive caddies in the front. Taking the case off, it's plain to see that these 8 disks are connected to SATA ports on the motherboard, there's no dedicated hardware RAID card in there. The CPU uses a passive cooler, so can't be anything too fancy (a recent Atom processor, I think), and has 2 GB of RAM installed. The server runs some kind of Linux-based OS. Several people on this forum have obviously found the performance of these devices just fine as they were recommended in a couple of recent threads where people were asking about storage servers. The server offers iSCISI, so must be capable of good enough performance to act as a VM disk image host. If the above is correct, is it likly that the QNAP server is using Linux's standard mdadm software RAID to run its RAID array, or are they likly to have had to write their own RAID system of some kind? If performance of mdadm RAID is up to running an iSCISI server, why do people bother buying hardware RAID cards in the first place? Is there likly to be some practical limit to the number of disks mdadm RAID will be able to handle - is 8 maybe the most you should expect to be able to use? -- David Hicks
Soulfish Posted January 17, 2011 Posted January 17, 2011 Does ZFS need special (i.e. Sun-only) hardware support to work correctly / with realistic performance? I tried using ZFS on a Linux system running on commodity hardware but got corrupted files - is this likly to have been the Linux implementation of ZFS, the hardware not being up to the job in some way, or something else? -- David Hicks You can run ZFS on anything that supports Solaris/FreeBSD. The Linux implementation isn't great, but the FreeBSD implementation is meant to be quite good if you don't want to run Solaris. If you want a nice easy to use distro with ZFS support built in have a look a Nexenta. Couple of options there if you have less than 12tb storage then Nexenta Community Edition comes with the same GUI as the Nexenta commercial product I believe and is free to run. If you have more than 12tb you can use Nexenta Core which is free for any amount of storage but doesn't have a GUI. If you need a GUI you could always use napp-it.org 1
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