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Which OSS Clustered Filesystem Should I Use?
Dishwasha writes "For over a decade I have had arrays of 10-20 disks providing larger than normal storage at home. I have suffered twice through complete loss of data once due to accidentally not re-enabling the notification on my hardware RAID and having an array power supply fail and the RAID controller was unable to recover half of the entire array. Now, I run RAID-10 manually verifying that each mirrored pair is properly distributed across each enclosure. I would like to upgrade the hardware but am currently severely tied to the current RAID hardware and would like to take a more hardware agnostic approach by utilizing a cluster filesystem. I currently have 8TB of data (16TB raw storage) and am very paranoid about data loss. My research has yielded 3 possible solutions: Luster, GlusterFS, and Ceph."
Read on for the rest of Dishwasha's question.
"Lustre is well accepted and used in 7 of the top 10 supercomputers in the world, but it has been sullied by the buy-off of Sun to Oracle. Fortunately the creator seems to have Lustre back under control via his company Whamcloud, but I am still reticent to pick something once affiliated with Oracle and it also appears that the solution may be a bit more complex than I need. Right now I would like to reduce my hardware requirements to 2 servers total with an equal number of disks to serve as both filesystem cluster servers and KVM hosts."
"GlusterFS seems to be gaining a lot of momentum now having backing from Red Hat. It is much less complex and supports distributed replication and directly exporting volumes through CIFS, but doesn't quite have the same endorsement as Lustre."
"Ceph seems the smallest of the three projects, but has an interesting striping and replication block-level driver called Rados."
"I really would like a clustered filesystem with distributed, replicated, and striped capabilities. If possible, I would like to control the number of replications at a file level. The cluster filesystem should work well with hosting virtual machines in a high-available fashion thereby supporting guest migrations. And lastly it should require as minimal hardware as possible with the possibility of upgrading and scaling without taking down data."
"Has anybody here on Slashdot had any experience with one or more of these clustered file systems? Are there any bandwidth and/or latency comparisons between them? Has anyone experienced a failure and can share their experience with the ease of recovery? Does anyone have any recommendations and why?"
"GlusterFS seems to be gaining a lot of momentum now having backing from Red Hat. It is much less complex and supports distributed replication and directly exporting volumes through CIFS, but doesn't quite have the same endorsement as Lustre."
"Ceph seems the smallest of the three projects, but has an interesting striping and replication block-level driver called Rados."
"I really would like a clustered filesystem with distributed, replicated, and striped capabilities. If possible, I would like to control the number of replications at a file level. The cluster filesystem should work well with hosting virtual machines in a high-available fashion thereby supporting guest migrations. And lastly it should require as minimal hardware as possible with the possibility of upgrading and scaling without taking down data."
"Has anybody here on Slashdot had any experience with one or more of these clustered file systems? Are there any bandwidth and/or latency comparisons between them? Has anyone experienced a failure and can share their experience with the ease of recovery? Does anyone have any recommendations and why?"
RAID is not a backup solution!
Is the only reason you're looking at a clustered filesystem that you don't want to lose data? Because if it is, it's probably not what you want. The purpose of a clustered filesystem is to minimize downtime in the face of a hardware failure. You still need a backup in the case of a software failure or in case you fat finger something, because a mass deletion can replicate to all copies.
20 disks seems like overkill for your storage needs. Seems like the more disks you use the greater the risk of failure of one or more of them. Also, your electricity bill must be through the roof. I have 4 3TB drives with a 3Ware controller in RAID5 array which gives me the same storage capacity with 1/5th the drives Aren't you making this more complicated than it needs to be? ...Maybe that's the point?
...I just came for the free beer.
LVM, mdadm & Ext4 or ZFS seems like it would be more then adequate for this. A 2U server can hold 36TB of raw data with software raid and consumer disks. 2.5" would be preferable for home use considering power usage unless your a fellow Canadian; in which case servers make great space heaters.
Uh... he DID confess to the crime AND lead the cops to his wife's body. I know...sarcasm, right?
...I just came for the free beer.
You ask about the technical specifications; but, when commenting regarding the three likely candidates you found, you've put philosophical objections first and foremost. I think you first need to figure out which factor is more important to you - specs, or philosophy. Otherwise you're probably going to waste a lot of time arguing in circles.
#DeleteChrome
How about ZFS with your RAID controllers in single drive mode (or worst case JBOD)? Let ZFS handle the vdevs as mirrors or raidz1/2 as you wish. ZFSforLinux is rapidly maturing and definitely stable enough for a home nas. Or go the OpenIndiana route if that's what you're comfortable with.
My 4TB setup has actually been a joy to maintain since committing to ZFS, with BTRFS waiting in the wings. The only downside is biting the bullet and using modern CPUs and 4-8GB memory. Recommissioning old hardware isn't the ideal way to go, ymmv.
Just a thought.
We have been using OCFS (Oracle Cluster File System) for some time in production between a few different servers.
Now, I am not a sysadmin so can't comment on that aspect. I'm like a product manager type, so I only really see two sides of it: 1) when it is working normally and everything is fine 2) when it stops working and everything is broken.
Overall from my perspective, I would rate it as "satisfactory". The "working normally" aspect is most of the time; everything is relatively seamless - we add new content to our servers using a variety of techniques (HTTP uploads, FTP uploads, etc) and they are all magically distributed to the nodes.
Unfortunately we have had several problems where something happens to the node and it seems to lose contact with the filesystem or something. At that point the node pretty much becomes worthless and needs to be rebooted, which seems to fix the problem (there might be other less drastic measures but this seems to be all we have at the moment).
So far this has JUST been not annoying enough for us to look at alternatives. Downtime hasn't been too bad overall; now we know what to look for we have alarming and stuff set up so we can catch failures a little bit sooner before things spiral out of control.
I have very briefly looked at the alternatives listed in the OP and look forward to reading what other reader's experiences are like with them.
I was going to say Lustre, but then I saw that you only have 16TB. 15 years ago that would have been impressive, but these days, those supercomputers you mention probably have that much in DRAM, and their file storage is in the multi-petabyte range. Lustre is optimized for large scale clusters, in which you have entire nodes (a node is a computer, here) dedicated to I/O - bringing external data into the in-cluster network fabric, while other nodes are compute nodes - they don't talk to the outside world, except by getting data via the I/O nodes.
That's why you'll see all this talk of OSSs and OSTs, as though they'd be distinct systems - on a large scale cluster they are.
For only 16TB, what you want is a SAN, or maybe even a NAS.
If you want open source, then go with openfiler. It supports pretty much everything. I haven't stress tested it, but it seems to work well for that order of magnitude of data.
You will spend all this effort to build this solution... and then your house will catch fire.
On the good side, the fire department WILL manage to save the basement by filling it with 80,000 gallons of water at 2,000GPM per fire engine.
Or, you'll be wiped out by a flood. Or a drunk will drive through the side of your house. Or you'll have a gas leak and the house will detonate. Or carpenter ants will eat away the floor joists.
Raid is not a backup solution. Neither is replication... if you whack the data, it'll likely be replicated. If you get a compromised machine somewhere, files they touch will likely be replicated. They only thing you're creating is an overly complex hardware mitigation. If THAT is how you define "data preservation"... you're doing it wrong.
Look more for a solution to move stuff offsite - a cheap pair of N routers running Tomato or OpenWRT, to a neighbor's house, and you reciprocate with each other. Bonus points if you use versions, transaction logs, journals, etc.
help me i've cloned myself and can't remember which one I am
Lustre is pretty cool, but it's not magic pixie dust. It won't break the laws of physics and somehow make a single node faster than it would be as a NFS server. It's for situations when a single file server doesn't have the bandwidth to handle lots of simultaneous readers and writers. A "small" Lustre filesystem these days usually has 8-16 object storage servers serving mid-high tens of TB. The high end filesystems have literally hundreds of OSSes and multiple PB served. The largest I know of right now is the 5PB Spider filesystem at Oak Ridge National Labs.
One nice thing about Lustre on the low end is that you can grow it... Start out small and add new OSSes and OSTs as you need them. This often makes sense in Life Sciences and digital animation scenarios where the initial fast storage needs are unknown or the initial budget is limited (but expected to grow). But if you're never planning to get beyond the capacity of a single node or two, Lustre is just going to be overhead. I don't know much about the other clustered filesystem options.
A host is a host from coast to coast...
Unless it's down, or slow, or fails to POST!
What kind of performance are you after? If you're not after anything over 40MB/S, I'd go for unRAID. I use this at home and it's brilliant. I've replaced many drives over the years, and I've had two hard drives fail with no massive consequences (data isn't striped). Plus, many many plugins are now available. SimpleFeatures (replacement gui), Plex Media Server, SQL, Email notifications with APCUPSD support etc etc.
I have to ask...
I'll go out on a limb and say it is just hoarding behavior. I wouldn't be surprised if slaker (53818) has a whole bunch of other stuff, besides data, but at least the data hoarding takes up less room than books, and isn't as sick as animal hoarding...
Having observed some hoarders, first hand, I think something goes off in their head that is like a "gotta collect them all" flag. It usually is concentrated on a favorite subject, but it could even be set off with garbage, like tearing open a package and setting down the wrapper... one is trash, but, if it is not discarded, the second one is the "start of a collection", and off they go.
This issue is a bit more complicated than you think.
If you're looking to have any kind of decent performance in your VMs this just won't work.
I've worked with VMs on all different kinds of storage (fiber channel SAN, local disk, iSCSI SAN (over 1Gb and 10Gb ethernet), Local hardware raid, NFS file shares, GFS2 (as in the RedHat cluster file system), and MooseFS and GlusterFS) All of these have been either in large test labs or in production cloud deployments. I've never had a cluster file system get close to passing muster as a storage medium for VM usage. IO is the number 1 bottleneck in virtualized environments, and these schemes just add completely unacceptable latency and bandwidth restrictions.
The only way to really run VMs is fiber channel SAN, local disk (or hardward raid), or iSCSI with 10GbE (on the storage server side). Even iSCSI with 2GbE (2x1GbE bonded) is not speedy enough to support more than 5-10 VMs running concurrently. You'll start to see problems at 5 VMs if the VMs are windows... For whatever reason Windows really likes to write to the disk. Currently I have 4 servers in my basement, a single storage server (6 2TB drives in a raid6, giving 8TB of usable disk) and 3 VM servers (2 2TB drives each, in hardward RAID1). I run the VMs locally and back them up to the storage machine over iSCSI nightly. I also have a shared volume on the storage system that all VMs and my household computers can access. I use openfiler for my storage system, if I had the money it would be nice to get a second storage server and replicate it (which openfiler supports), but I don't have that cash just sitting around right now
Backing up 8TB of data (ok, so I have about 5TB used), is basically impossible offsite, so we have a "special" folder on the shared drive that is backed up using crashplan, its about 600GB, and the first backup took nearly 3 months over a 5mbps upload.
The above setup is the only one I've found that is both a) somewhat affordable, and b) performs well enough to do actual work in the VMs. It provides for some mobility in the event of a hardware failure (if a VM server crashes, I can run the crashed VMs via iSCSI on another server (from the day old backup), If the storage server crashes, the only "important" data is the 600GB in the special folder... which would take 2 months to download over my home connection... But could be downloaded in stages, IE get the most important stuff immediately). If both a vm server and the storage server crash, I'm out the VMs that were running on the vm server, but again the important data is off-site, and the VMs can be rebuilt in a day or less.
I would be grateful if this bit of 'humour' could not be posted to *every single vaguely cloud-related post*.
http://linux.slashdot.org/comments.pl?sid=2356014&cid=36928876
http://tech.slashdot.org/comments.pl?sid=1683582&cid=32542918
http://tech.slashdot.org/comments.pl?sid=2499970&cid=37882212
http://it.slashdot.org/comments.pl?sid=2489600&cid=37805882
Christ. It was only mildly amusing to begin with, let it go.
Those filesystems are not designed primarily with your scenario in mind. If you want a hardware agnostic support, use software RAID or a non-cluster filesystem like ZFS.
Distributing your storage will probably not enhance your ability to survive a mishap. In fact, the complexity of the situation probably increases your risk of messing up your data (I have heard more than a couple of instances of someone accidentally destroying all the contents of a distributed filesystem, but in those professional contexts they have a real backup strategy. You'll be pissing away money on power to drive multiple computers that you really don't need to power.
If you care about catastrophic recovery, you need a real backup solution. This may mean identifying what's "important" from a practical home situation. If you don't mind downtime so long as your data is accessible in a day or two (e.g. time to get replacement parts) without going to your backup media and without suffering the loss of non-critical data, then also having a software raid or ZFS is the way to go. If you want to avoid downtime (within reason), get yourself a box with basic redundancy designed into it like a tower server from Dell/HP/IBM. If Intel, you would sadly want to go Xeon to get ECC, on AMD you can get ECC cheaper. In terms of drive count, I'd dial it back to 4 3TB drives in a RAID5 (or 5 in RAID6 if you wanted), safe on power and reduce risk in the system.
XML is like violence. If it doesn't solve the problem, use more.
Two issues here:
1. You're approaching the problem from the wrong angle. IMV, the angle you take should be "how long can can I afford to be without this data and how much money am I prepared to throw at a solution?" rather than "what technology exists that I can use to make the system more reliable?". Taking the former approach allows you to plan exactly how you'd deal with data loss - whether it's through human error, software/hardware failure, fire, theft, flood or what have you. Taking the latter approach tends to result in some whacking great Heath Robinson (or if you're American, Rube Goldberg) of a solution that still has a whacking great hole in it somewhere.
2. 8TB of data is not an enormous amount by any modern standard. You can buy a NAS box off-the-shelf today that will take 12x3TB hard disks for 36TB (18TB if you've got the good sense to run them in a RAID 1+0 configuration) of storage; at this level they typically have replication built right into them so you can buy two and replicate one to the other (though like all replication-type solutions, it's not a form of backup and you mustn't treat it as such). If that doesn't appeal, simply put a couple of SATA controllers in a cheap box and run OpenFiler. Anything you cobble together yourself based on the latest clustered filesystem du jour will suffer from one huge flaw - a system that's designed to be highly-available is frequently less reliable than one that isn't, simply because you're making it that much more complicated that there's a lot more to go wrong.
STAY AWAY FROM DROBO!
I had a client ask me to set one up for them. You don't partition it like a standard raid array, you format it to some predetermined size that may be larger then the physical disk space in the machine (through their drobo dashboard). If you have three 1 TB disks you will have around 2TB of actual storage but you can format it for 16TB under Win 7. This is achieved via their "beyond raid" technology which fools the OS into thinking there is more disk space than there actually is. This lets the user make one large volume now and then add disks in the future, even disks of different sizes can be mixed and matched. If you start to go beyond the physical capacity, the array degrades and goes offline until you add another disk and wait hours or days for the disks to reorganize. My client was consolidating her photography library to the drobo when it just crapped out. Turns out she ran over the physical limit.
Then if your lucky, your computer be it Apple or Windows will take upward of 30 to 45 minutes to boot and shutdown if the fucking thing is plugged in and powered on during either of those two procedures. Drobo recommends you move your data to another set of disks and re-format your drobo. As if people have a few spare TB of disk capacity just sitting around, that's the reason they bought your shit box to begin with, assholes. Its a known issue.
I have personally used hardware raid 5, software block level raid 5 and ZFS. If you ask me id rather have the file system do the RAID work at the file system level, not the block level where the file system is ignorant of what lies beneath. ZFS is the way to go until BTRFS is fully stable and feature competitive with ZFS. Then you do incremental backups offsite, either to a family or friends house or to a commercial off site backup provider.
And what is your 16 TB consist of? If its movies and the like then don't bother spending money backing it up. If its self make video and other personal large files then that makes sense. I know of people who spent oodles of cash to backup silly crap like downloaded movies that can easily be replaced or rented from Netflix.
With the way things are going in the storage world, SSD's will eclipse mechanical disks at the desktop level and mechanical disks will be relegated to backup duty where they far outstrip SSD's in capacity. It reminds me of when tape drives were the king of capacity, often tapes were several orders of magnitude larger than current hard disks and tapes were cheap. They were slow but my god did they have capacity. Now it looks like SSD's will assume the role of desktop storage and to some degree server storage while mechanical disks will be used for large backup systems and file servers. Mechanical hard drives of today will be tomorrows tape drives and then obsolete when SSD's begin to overtake then in capacity. By then we might have something even higher in capacity like holographic or some other sci-fi sounding storage.