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by Greg Downing on Tue Oct 09, 2007 8:32 am
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I just ordered this enclosure and five 750GB SATA hard drives to go in it with the intention of creating a mirrorred configuration giving me 1.875 GB of storage with an eSATA connection to my desktop.

http://www.addonics.com/products/raid_system/ast4.asp

(model ST5XHPM)

I will be using it with this controller:

http://www.addonics.com/products/host_c ... sa4r-e.asp

My question is which RAID configuration would folks suggest I use? I was figuring on simple RAID 1 but would like some input before I set it all up.

With RAID 1 and an odd number of drives (5 in my case) do I still get 50% capacity?

Should I consider RAID 0+1?
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by E.J. Peiker on Tue Oct 09, 2007 9:05 am
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With RAID 1 you will only be able to use 4 of the drives. I think RAID 5 is probably the best option if you want to use all 5 drives. You would get 3TB of storage with the 5th drive also in use. Most RAID 5 installations use 3 drives but it should be possible to do with 5 assuming the RAID conroller allows this.

Alternately, you could go with RAID 1 and get 1.5TB of storage and have the 5th drive in waiting in case you ever need to swap out one of the bad ones.

RAID 0+1 would also make use of just 4 drives. Only RAID 0, RAID 3 and RAID 5 can make use of an odd number of drives. RAID 3 is not something I would recommend as it puts all of the parity info on a single drive while RAID 5 spans the parity data among multiple drives.
 

by Greg Downing on Tue Oct 09, 2007 9:36 am
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Thanks EJ, that is what I needed to know. I am looking at another controller that offers RAID 5. I am going to call the place and make sure this is supported for 5 drives as the literature is a little confusing and I was unsure about the odd number of drives.
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by Royce Howland on Tue Oct 09, 2007 10:07 am
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I would also opt for the RAID5 config, Greg. It makes the best "bang for buck" use of your hard drives, giving a good blend of performance, storage capacity, and protection from single-disk failures. For capacity, RAID5 always gives the N-1 disks worth of actual storage, where N is the number of disks in the RAID set. RAID1 (or RAID0+1) always gives you N/2 disks worth of storage (i.e. 50%), which reduces the "bang for buck" by a lot.

RAID0+1 is most often used as an alternative to RAID5, when people want the best possible "money is no object" performance while still having full redundancy in case of disk crashes. Personally, given the speed of current disks & hardware, I think the extra performance is less relevant to anyone not working with video, which is why I go with RAID5.

My RAID5 configs typically use 4 drives, providing 75% of the storage. In your case with a 5 drive setup you would get 80% of the storage. You could also keep 1 drive on the side as a backup as E.J. mentions. This is what I did when I set up my Infrant RAID5 boxes. Each one has 4x500GB installed, for 1.5TB of net space. And I have a 5th 500GB disk on the shelf as a replacement for when one of the hot disks goes down...
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by danator on Tue Oct 09, 2007 10:23 am
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Any chances that you have better interface on you station than the legacy pci-32 bits?? Like pci-e or pci-x 64-133? You array gonna be slower than nowsaday firewire raid. Might well get a cheap NAS.
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by Greg Downing on Tue Oct 09, 2007 3:13 pm
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5 x 750GB drives in a RAID 5 config gives me 3TB of storage. Isn't there a 2TB limitation in XP and is there any way around it? Can I partition these into 2 x 1.5TB partitions?
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by Bob Ettinger on Tue Oct 09, 2007 3:28 pm
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Greg,

Keep us updated as this progresses. It is a projerct I for one would like.
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by Royce Howland on Tue Oct 09, 2007 5:48 pm
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Greg, Windows XP (32-bit editions) are limited to 2TB per partition if the disk is a "basic disk". In this case you can simply make 2 partitions if that works for you.

I believe another thing that can be done is to convert the disk from a "basic disk" to a "dynamic disk", using the Windows disk manager. This permits a larger cluster size to be selected when you format for NTFS, which in turn permits an increased volume size -- up to 16TB can be achieved using a 4KB cluster size according to what I've read. To enable this, make sure your RAID controller itself will allow you to create the RAID volume with >2TB. The controller would have to have what's called 64-bit LBA support; if it doesn't then it also might be limited to volumes of 2TB.

So with a dynamic disk and 64-bit RAID controller, I think you could get all the storage into a single Windows volume. Dynamic volumes have some limitations, for example I think they can't be used on portable storage connected by USB or Firewire. I'm not sure if the same limit applies to eSATA connected storage or not. Does anybody know of any downside in using a dynamic volume for this?
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by Greg Downing on Tue Oct 09, 2007 6:29 pm
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Thanks Royce,

I will probably partition the space. Another alternative, which was suggested by the tech where I bought the box, was to use only 3 drives in a RAID 5 configuration and then mirror that to the remaining two. That would give me 1.5 TB of space in RAID 5 with an internal secondary backup.

OR, I could just keep it simple and use RAID 1 like I originally planned and use 4 disks instead of 5 - still giving me 1.5TB

The kicker is that 1.5TB does not give me much room to grow - I am at 1.25 TB right now.

Just an FYI that I also plan to have the entire volume backup up using externals and stored on site (unless I do the secondary internal backup as described above). In addition I will have a second back-up onto externals off site as well - no matter what.

What to do....lol
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by Royce Howland on Tue Oct 09, 2007 6:49 pm
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IMO, definitely go with RAID5 using 4 or all 5 of your disks, since your backup to additional media is covered by your other options. For me, in the general case RAID1 just bites too deeply into the available capacity. I do use RAID1 in limited situations, usually just for single disks where a hard failure would be a major PITA. (E.g. the boot disk on my servers.) But for big storage, mirroring with RAID1 is an expensive proposition... my paranoia seeks other outlets.

As for "internal backup", backup disks within the identical disk cabinet are of dubious value I feel. In terms of big hardware or software failures, site disasters, theft, etc. it seems likely that most events that could take out the RAID5 volume would also take out the mirrored backup volume living in the neighboring slots. Any human error committed on the RAID5 data also will be instantly propagated to the mirrored storage, so you're not even protected against minor slips that you detect a few seconds or minutes later. I prefer my backups to have a reasonable chance of surviving the initial problem that made me go to them to recover something! :)

And as you say you need more growth room... :lol:
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by Bob Bell on Tue Oct 09, 2007 6:53 pm
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Greg your posts are like some of our project meetings at work. Too bad I can't send you to our storage engineering group but they would probably talk you into a $40,000 mirrrored raid 10 SAN with 99.999% availability :)

Back to your issue, Most home / small business storage cases hold 5 drives, when you move past that class into storage arrays you can get rack mount (or put on a flat surface) drive arrays that hold 12, 16, 32 and on drives. I think it would be a poor move to build a storage array that would be 80%+ full on turn up. You are forcing yourself to go through this again early next year or break your image library onto multiple arrays and dealing with backing that up.

The other thing is I would consider moving to a NAS / SAN enviroment instead of eSATA or something plugged into 1 PC. You can set them up on a 100/1000 network, have network management tools and the files would be accessible by any machine on the network given the correct authentication.
 

by Greg Downing on Tue Oct 09, 2007 7:03 pm
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Bob,

I considered NAS but I just cannot live with the performance hit. This is why I went the route I did. Plus, I can still access the volume over the network and even map it as a drive on my other machines with the same performance as a NAS. On the primary machine, where I do most of my editing, I will have much better performance than with a NAS.

Royce,

I think I will do that. I have one more question. If I use 4 (or even 3) drives in a RAID 5 config, can I later add another drive to the array to increase the capacity or would I need to reformat and start over again? If the answer is yes, I can add a drive later, then I will likely start with 4 drives and use the 5th as a spare or for something else.
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by Greg Schneider on Tue Oct 09, 2007 7:09 pm
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If you are having issues fitting all the discs into the enclosure, I'd buy a large server case with plenty of room for drives, put some components (CPU, RAM etC) in there as well as a RAID card with 8+ ports.

If you have a Gigabit network there should be just about nil performance difference than having it hooked up directly.
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by danator on Tue Oct 09, 2007 8:27 pm
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Royce Howland wrote:Greg, Windows XP (32-bit editions) are limited to 2TB per partition if the disk is a "basic disk". In this case you can simply make 2 partitions if that works for you.

I believe another thing that can be done is to convert the disk from a "basic disk" to a "dynamic disk", using the Windows disk manager. This permits a larger cluster size to be selected when you format for NTFS, which in turn permits an increased volume size -- up to 16TB can be achieved using a 4KB cluster size according to what I've read. To enable this, make sure your RAID controller itself will allow you to create the RAID volume with >2TB. The controller would have to have what's called 64-bit LBA support; if it doesn't then it also might be limited to volumes of 2TB.

So with a dynamic disk and 64-bit RAID controller, I think you could get all the storage into a single Windows volume. Dynamic volumes have some limitations, for example I think they can't be used on portable storage connected by USB or Firewire. I'm not sure if the same limit applies to eSATA connected storage or not. Does anybody know of any downside in using a dynamic volume for this?
You can't get over 2TB with Basic/Dynamic disk. Windows added GUID Partition Table (GPT) option with 64 bits OS & also available on 2k3 sp1 to expand 2TB volume to 256TB. The problem is xp 32 doesn't read GPT partition if i remember correctly, that could post a backward compatibility issue with the rest of the system.
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by Royce Howland on Tue Oct 09, 2007 9:54 pm
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Daniel: Win XP 32-bit edition doesn't do the GPT stuff, so you're right on that. I was under the impression that a dynamic disk could do >2TB without GPT however, even on the 32-bit edition of XP, since 2^32 (minus 1) clusters with cluster size of 4K (the default for dynamic disks) is 16TB. However I could be wrong on this, I don't have such a large spare volume sitting around to conduct a test. :) And the Microsoft (and other) docs I've re-read this evening seem ambiguous in many cases.

However one piece of blurbage I found stated the following specs for Win XP Pro 32-bit Edition with SP1 or later:
  • - 4 GB of Virtual Memory
    - 2 TB NTFS Partition (Basic Volume)
    - 16 TB minus 64 KB NTFS Partition (Dynamic Volume - 4 KB Cluster Size)
    - 256 TB minus 64 KB NTFS Partition (Dynamic Volume - 64 KB Cluster Size)
    - > 137 GB Hard Disks require SP1 or higher (48-bit LBA-compatible BIOS Required)
The same page states the following for Win XP Pro 64-bit Edition:
  • - 16 TB of Virtual Memory
    - 2 TB NTFS Partition (Basic Volume)
    - 16 TB minus 64 KB NTFS Partition (Dynamic Volume - 4 KB Cluster Size)
    - 256 TB minus 64 KB NTFS Partition (Dynamic Volume - 64 KB Cluster Size)
    - 18 EB NTFS Partition (GPT Volume)
That seems definitive to me, although it could be incorrect. :) I don't recall now exactly where I cribbed that info, I thought it was a Microsoft page but it might have come from elsewhere.

A Microsoft tech note does state the following:
  • In theory, the maximum NTFS volume size is 2^64 clusters minus 1 cluster. However, the maximum NTFS volume size as implemented in Windows XP Professional is 2^32 clusters minus 1 cluster. For example, using 64-KB clusters, the maximum NTFS volume size is 256 terabytes minus 64 KB. Using the default cluster size of 4 KB, the maximum NTFS volume size is 16 terabytes minus 4 KB.

    Because partition tables on master boot record (MBR) disks support only partition sizes up to 2 terabytes, you must use dynamic volumes to create NTFS volumes over 2 terabytes. Windows XP Professional manages dynamic volumes in a special database instead of in the partition table, so dynamic volumes are not subject to the 2-terabyte physical limit imposed by the partition table. Therefore, dynamic NTFS volumes can be as large as the maximum volume size supported by NTFS.

    64-bit computers that use GUID partition table (GPT) disks also support NTFS volumes larger than 2 terabytes.
This info is from the following page:
http://technet.microsoft.com/en-us/libr ... 57112.aspx
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by Royce Howland on Tue Oct 09, 2007 10:01 pm
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Greg Downing wrote:If I use 4 (or even 3) drives in a RAID 5 config, can I later add another drive to the array to increase the capacity or would I need to reformat and start over again? If the answer is yes, I can add a drive later, then I will likely start with 4 drives and use the 5th as a spare or for something else.
I believe expanding a standard RAID volume just by adding a disk normally is not possible because all of the striped, mirrored and/or parity data spread across the disks would be thrown out of whack. My Infrant NAS boxes have a proprietary mode called "XRAID" that is dynamically expandable just by adding disks, and this was/is a major selling feature of their kit. In some cases expanding a normal RAID volume may be possible, if the volume is managed by some kind of software volume manager that can dynamically rebuild the RAID striping & mirroring data based on adding a new disk into the mix. This is basically what the Infrant boxes are doing, because they are really small Linux servers running volume management software. Depending on the volume manager in question, there may be some limitations to this.

E.g. in one case of a volume manager I recall, if I'm not mistaken, a new disk could be added to a RAID5 volume but the new disk's data was not included in the parity information so that disk's data was not protected by the RAID5 redundancy. This basically concatenated a RAID5 volume with a non-RAID volume and made them appear to Windows as a single volume, but with different underlying characteristics depending on what data lived on which disk. Dangerous IMO.

Personally I find it best to size a RAID volume exactly where I want it, to start. If I need to grow, I grow by creating a completely new volume using new disks (usually cheaper, faster, larger, etc. by then) and copy the old one to the new one. I then either retire the old one, or repurpose it for something else.

Check the documentation for your RAID controller and see if it permits any kind of dynamic volume management. If not, go big to start :) and plan to grow by adding a new, separate RAID5 volume down the line.
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by Bob Bell on Tue Oct 09, 2007 10:10 pm
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Royce,

I am mostly on the Data / Voice side so I don't spend much time with OS's, but I thought XP PRO supported a max of 4 GB of ram, 2GB of Virtual Memory for the system and 2 GB for each additional Process. That would would the Virtual memory way over 4GB for a 32bit XP system.

The raid controllers we use on our systems, let us use hot spares if the HD is built by the specific raid controller. Meaning we cannot swap drives between systems without running the utilities first. I am guessing this is controller specific and we use mostly HP and IBM blades. If I remember correctly, HP controllers put some kind of ID on the hard drive somewhere with config and controller serial number or something like that.

I have looked at Infrant NAS devices but haven't found anyone with personal experience before. How do you like them?
 

by Royce Howland on Tue Oct 09, 2007 10:35 pm
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Bob: Sorry, the virtual memory business was a bit of extra fluff I just copied & pasted with the other disk capacity info. I don't want to derail the thread into the whole Windows RAM/VM issue. :) But to digress briefly, VM is split into two parts -- Windows space and application space. Normally as you say it's 2GB each, for a total of 4GB of VM. Using the /3GB switch discussed at length in another thread here, you can alter the balance to 1GB of VM for Windows and 3GB for the application, still a total of 4GB. Yes, you can have more than one process running, each of which gets its own 4GB of VM... that's why the Windows page file can get really large. :) But this isn't really considered as having "way over 4GB" of VM, since useful work that you can do needs a running process to do it, and each process can only have 4GB total.

Hot spares are something we haven't touched on yet in a RAID configuration. A "cold spare" is an extra hard disk sitting in a box or on the shelf, which is manually swapped into a RAID configuration to replace a disk that died. As you note, many RAID controllers actually will let you designate a hot disk as a spare... i.e. they put the RAID volume database & admin information on the disk, but don't actively use it for data striping/mirroring or parity data. The disk is alive, but it's unallocated. If the RAID controller detects that an allocated disk in the RAID set has become toast, then it can rebuild the dead disk's information onto the hot spare using exactly the same mechanics as would be used to rebuild the dead disk if it was physically removed and replaced with a new disk. In the hot spare scenario, when the dead disk is pulled and replaced, its replacement normally becomes the new hot spare.

Because the hot spares are known to the RAID controller and have the RAID set's config info written to them, this is why you often can't just swap those spare disks between different RAID groups. Even though they're not allocated for any data use, they are "tagged" to a specific RAID set.

I normally don't mess with hot spares since my requirements aren't truly 7/24. :) Cold spares on the shelf are good enough. If a disk blows it will take me a few hours to swap it, but in the meantime I'm saving a lot of platter spin time on a disk that isn't actively in use for storage. And since I have several RAID and single disk systems all based on the identical Seagate 500GB Nearline disks, a couple of cold spares can cover them all.

Re: the Infrant boxes, I do like them. There is some goofy stuff about them, largely caused due to my mixed environment of Windows and UNIX systems that are being simultaneously served by the NAS boxes using a combination of CIFS/samba, NFS and rsync. :) But with a few minor annoyances, they do exactly what I want and perform well as secondary storage for my photo stuff (my workstations all have fast 500GB local disks that I use for primary working storage). The NAS boxes even act as a big chunk of primary storage for some of my UNIX servers where screaming I/O is not a big deal. E.g. my web sites are served from Infrant NAS volumes mounted on old Sun UNIX boxes via NFS...
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by E.J. Peiker on Tue Oct 09, 2007 11:37 pm
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Greg, no you can not just add another volume to a RAID 5 due to the parity striping. What you can do though, is to add another drive, reconfigure the RAID array, reformat and then copy all of the data back onto the newly configured RAID 5 system. It will take a long time though. Also, if you lose one of those 750GB drives, be prepared for pretty much a whole day of disk grinding for the array to rebuild itself with all of the data intact after you swap in a new drive.

BTW, another thought on the 2TB route is just to get 4 1TB Hitachi drives instead of the 5 750GB drives and then do a RAID 0+1. Cost should be about the same and it will be slightly better performing (although probably not noticeable)
 

by GeneO on Wed Oct 10, 2007 8:47 am
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Greg Downing wrote:I just ordered this enclosure and five 750GB SATA hard drives to go in it with the intention of creating a mirrorred configuration giving me 1.875 GB of storage with an eSATA connection to my desktop.

http://www.addonics.com/products/raid_system/ast4.asp

(model ST5XHPM)

I will be using it with this controller:

http://www.addonics.com/products/host_c ... sa4r-e.asp

My question is which RAID configuration would folks suggest I use? I was figuring on simple RAID 1 but would like some input before I set it all up.

With RAID 1 and an odd number of drives (5 in my case) do I still get 50% capacity?

Should I consider RAID 0+1?
Raid 1 will give you 1/2 the space on all of the drives since it is mirroring I think you will only be able to use four for 1.5 TB. You can use the fifth as a hot spare (Raid 1+S) - the controller is good, it will automatic rebuild from the hot spare. I reccommend you always use a hot spare - double failures will occur (actually are likely).

Raid 10 (1+0) will give you better performance because of the striping, but it looks like that card doesn't support Raid10 with a hot spare.

Raid 5 on that card isn't supported. If you can get a raid 5 card, it will give redundancy at the cost of only one drive for the parity (plus a hot spare if you choose), so it would give you 3 TB (2.25 TB with a hot spare). You suffer on writes because you have to calculate and write the parity.

Better yet is raid 6 which basically stripes the parity so you get better performance than raid 5 and it can also recover from the failure of two drives.

- Gene

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