• February 24, 2025, 12:17:00 AM
  • Welcome, Guest
Please login or register.

Login with username, password and session length
Advanced search  

News:

This Forum Beta is ONLY for registered owners of D-Link products in the USA for which we have created boards at this time.

Author Topic: RAID 1 rebuilds slowly  (Read 10218 times)

rgiaco777

  • Level 1 Member
  • *
  • Posts: 3
RAID 1 rebuilds slowly
« on: December 19, 2009, 08:29:37 PM »

Hi all,

I've had my DNS-321 for a few days now and for the most part am very happy with it.  I'm running a RAID 1 array with 3 Western Digital WD10EADS 1TB drives (I plan to switch one drive out every month or so and keep it offsite for extra data security).So far I've been experiencing typical data transfer speeds to/from the computers on my network (8MB/s with 10/100 ethernet and ~1MB/s over wireless G).  

However, I've tried pulling a drive and replacing it with the other to see how the DNS-321 handles a degradation in RAID.  The new drive formats as normal, but the RAID rebuild occurs EXTREMELY slowly.  I have slightly more than 1GB on the drive, and it's taking me 3 hours to rebuild that 1GB.  When I had 200GB on the drive and tried a rebuild, it gave me an estimated sync time of 15,000 minutes (this is around 10 DAYS! :o)

Is this just the nature of RAID on these D-Link boxes, or is something amiss?  I don't know what to expect for sync time, but this strikes me as REALLY slow.

Thanks!
Ryan
Logged

JoeSchmuck

  • Level 3 Member
  • ***
  • Posts: 231
  • Retired Rocket Scientist
Re: RAID 1 rebuilds slowly
« Reply #1 on: December 20, 2009, 05:54:24 AM »

It's sad to say but this is normal.  This has nothing to do with your drives, there is not a lot of horsepower under the hood of this NAS so the 10 days was a bad estimate and the time should have dropped as the NAS proceeded.  Although I have only had two rebuilds, only one took more than 5 hours.  I've heard of some rebuilds taking over night as well.

So, to answer your question, it's normal.  You get what you pay for and this is a nice entry level NAS for home use.  I'd never use this in the office with a shared computer, again, low horsepower.

Might I make a recommendation on the method of your backup...  Since it sounds like you are not even close to filling your TB drives, go buy two USB 750GB (or whatever capacity you think you will need) external drives.  Leave one off site, hook the other to your computer and copy all the data from the NAS to the USB drive.  There are programs out there that will keep the files in sync so you don't have to sit around waiting for the copy to occur.  Then every month swap out the external USB hard drive.  The sync program will automatically resync everything and you are done.

I just wouldn't recommend swapping drives in and out of the NAS that frequently.  I doubt it's built for that kind of frequent use.

I hope this gives you something to think about.

-Joe
Logged

gunrunnerjohn

  • Level 11 Member
  • *
  • Posts: 2717
Re: RAID 1 rebuilds slowly
« Reply #2 on: December 20, 2009, 08:40:58 AM »

A 900gig rebuild took about 16 hours on my DNS-321.
Logged
Microsoft MVP - Windows Desktop Experience
Remember: Data you don't have two copies of is data you don't care about!
PS: RAID of any level is NOT a second copy.

JoeSchmuck

  • Level 3 Member
  • ***
  • Posts: 231
  • Retired Rocket Scientist
Re: RAID 1 rebuilds slowly
« Reply #3 on: December 20, 2009, 09:56:58 AM »

A 900gig rebuild took about 16 hours on my DNS-321.
Yup, don't want to do that too often because if I recall correctly the NAS is not accessable during the rebuild process.  16 hours, wow!  I will say one thing for certain, the next NAS I buy will have more power but that also means I will have to shell out more money.  I mean, honestly this isn't a bad NAS and it sure beats leaving a power hungry PC on 24/7.
Logged

gunrunnerjohn

  • Level 11 Member
  • *
  • Posts: 2717
Re: RAID 1 rebuilds slowly
« Reply #4 on: December 20, 2009, 10:11:12 AM »

Actually, I was able to access the files during the rebuild, but it was pretty slow access. :D
Logged
Microsoft MVP - Windows Desktop Experience
Remember: Data you don't have two copies of is data you don't care about!
PS: RAID of any level is NOT a second copy.

rgiaco777

  • Level 1 Member
  • *
  • Posts: 3
Re: RAID 1 rebuilds slowly
« Reply #5 on: December 20, 2009, 11:51:55 AM »

Thanks for all the help, everyone!  I would be willing to wait for an overnight rebuild, but anything longer than that would get agonizingly long.  I think what I'll do is buy a cheap enclosure for my 3rd 1TB drive and use it as USB/FireWire to back up the NAS offsite.

I've also noticed that I can access files during the rebuild, but it definitely is slow and it also slows down the rebuild itself (no surprise there).

I think I'm well on my way to having my storage solution figured out! :)
Ryan
Logged

gunrunnerjohn

  • Level 11 Member
  • *
  • Posts: 2717
Re: RAID 1 rebuilds slowly
« Reply #6 on: December 20, 2009, 12:03:43 PM »

The rebuild seems like it's taking way too long for the small amount of data...
Logged
Microsoft MVP - Windows Desktop Experience
Remember: Data you don't have two copies of is data you don't care about!
PS: RAID of any level is NOT a second copy.

JoeSchmuck

  • Level 3 Member
  • ***
  • Posts: 231
  • Retired Rocket Scientist
Re: RAID 1 rebuilds slowly
« Reply #7 on: December 21, 2009, 11:49:18 AM »

Guess I was too impatient to access my files.
Logged

mzpx

  • Level 2 Member
  • **
  • Posts: 25
Re: RAID 1 rebuilds slowly
« Reply #8 on: December 21, 2009, 01:27:57 PM »

I am not an expert (on this either), so don't blame me if I am wrong. Just correct me, if you know better.

The DNS-321 runs a Linux kernel with the 'md' (multiple devices) feature, which is a funny name for what we call 'raid'. It is called such as it creates a single device out of multiple devices. E.g. you have two drives and it creates a new, virtual device, which looks like it was a single HDD.

When you use MD to create a mirror, it effectively copies all the physical sectors from one drive to the other. It does this on the 'device' level, where it does not know anything about filesystems and such things. So if you have an 2x1 TB HDD and only 1MB data on it, it will still copy all the 1TB worth of sectors as it does not know (or care for) which sector is in use and which is not.

The downside of this is that it will spend a long time to build a mirror even on empty drives. (Just remember your initial build.) It also has to have two devices (partitions) of exactly the same size (number of sectors). If you replace a drive and the new has just one fewer sectors - it won't work.

The upside is that this mechanism does not care what filesystem you put on top of it, you can use ext2, ext3, NTFS, whatever. (The DNS-321 only supports ext2/3, but generally you are welcome to use anything over the MD layer.)

I do not KNOW how a mirrored raid with MD supports accessing the data WHILE it is building the mirror, but I assume that
- if you read data, it will read the 'good' side;
- if you write a sector that is in the already copied range, it will write both drives;
- if you write a sector that is in the not yet copied range, it will write the good side - this is touch dangerous since if this write fails, then your data is nuked;

Since it keeps the HDDs busy with the copy (build mirror) process it makes sense that other data access will be slow, although possible. Also since it will write through the whole bloody drive, it will make a lot of heat. I would recommend not to put on the cage cover until the rebuild is done. Using low power / low heat drives is a nice idea. For me a build / re-build (same thing) of a mirror of 2x 1.5TB drives was about an overnight, maybe more, but less than a full day. (I started at the evening, was still working on it at the morning, but finished by the next evening.) I am using low speed, low heat Samsung Spinpoint drives.

Having offsite backup is a GREAT idea, but - as someone had pointed out - as long as your data set is small you might be better off just copying it to another drive. I suspect it is possible to do this via the USB port to an external HDD, but I am not sure if the default firmware supports such functionality. You might either have to copy the data via the network (slow) or get into fun-plug hackery (not for the faint hearted, you can hose your data if you don't know what you are doing.).

BTW, if I am correct, then your rebuild time should not depend on how much data you have on the drive (it will copy all the sectors anyway). The estimate of 10 days is just an error, it will not take that long. (Except if your drives are faulty.)
Logged

mzpx

  • Level 2 Member
  • **
  • Posts: 25
Re: RAID 1 rebuilds slowly
« Reply #9 on: December 21, 2009, 02:14:52 PM »

Just one more comment on what JoeSchmuck mentioned about leaving a power hungry PC on 24/7.

I measured 6W power usage on my DNS-321 when idle and 16W when writing (with 2 mirrored low power drive).

I have an Intel SS4200 with 4 (not low power) HDDs in RAID5. It sucks up 35W while idle and up to 90W while working. If I was using only 2 low power drives that would be lower, of course, but still. Yes, it gives me 50+ Mb/s speed (w/o any jumbo frames) and costs only $135 (currently) at buy.com. (OK, when I bought it is was $150.)

Guess which one do I shut down when I leave from home? *smile*

I suppose there are other solutions using less juice and costing more. Still.
IMHO, for (most) home users the DNS-321 is just fine.
Logged

gunrunnerjohn

  • Level 11 Member
  • *
  • Posts: 2717
Re: RAID 1 rebuilds slowly
« Reply #10 on: December 21, 2009, 02:44:24 PM »

I have an Intel SS4200 with 4 (not low power) HDDs in RAID5. It sucks up 35W while idle and up to 90W while working. If I was using only 2 low power drives that would be lower, of course, but still. Yes, it gives me 50+ Mb/s speed (w/o any jumbo frames) and costs only $135 (currently) at buy.com. (OK, when I bought it is was $150.)
Point of curiosity.  Does this unit support both anonymous and password protected shares?  I see it for $135, it is tempting... :)

What issues have you had with it?
Logged
Microsoft MVP - Windows Desktop Experience
Remember: Data you don't have two copies of is data you don't care about!
PS: RAID of any level is NOT a second copy.

mzpx

  • Level 2 Member
  • **
  • Posts: 25
Re: RAID 1 rebuilds slowly
« Reply #11 on: December 21, 2009, 04:09:16 PM »

to gunrunnerjohn:

I just got it and I barely set it up. It runs Linux and it has SSH access, so if you are willing to edit the smb.conf file you can do pretty much anything that SAMBA is able to do. It is not rocket science.

It does have web interface to create users / groups and assign access privileges based on those to each share (shared directory) you create, but for home use I don't need any of that, so I can not give you any hands on info. (I always wonder when people write about troubles with the authorization on the DNS-321. Why don't they just leave it open? Who are they trying to protect the data in their home from?) BTW, it has support for Active Directory, so if you are a window server person and you run such thing at home, you can do that. (Again, I believe that is a SAMBA feature which is exposed via the web interface on the SS4200, so you might even get that working with the DNS-321 if you SSH into it and edit the samba config files. Assuming you need that level of user management.)

On my actual file server (which is yet another Linux machine) I keep important stuff (photo collection going back many years) read only, so it doesn't get deleted accidentally, but available to all. Backup areas are writable for all. To get data onto the r/o areas I have an upload area/share (writable for all) and then copy the data within the server while logged into the server. Doesn't take that much.

I got the SS4200 as a geek toy, put whatever drives I had around into it and just started playing around with it.

I am not happy with the power usage, but it supposed to be possible to send it to standby and use WOL to wake it when needed. This is a bit of a challenge to any OS, depending on drivers it can fail easily, so a tuned solution coming from EMC/Intel might do it more reliably than some home baked setup. (My current Linux server sure fails on that. I blame the NVidia driver.) I haven't tested this on the SS4200 yet, but according to what I read on the fan twiki, it works and someone had even wrote a windows util to do this easily / automatically. (When you boot your windows machine it sends a WOL to the server. When you shut down, it sends the server to sleep.)

FYI, the setup that Legendmicro sells via buy.com at $135 is actually (at least what I got) a SS4200EHW (bare hardware) branded by a large boxmaker, who sold it originally with WHS (that is Windows Home Server). Legendmicro got the leftover bare boxes w/o any HDDs, added a 256MB DOM module, onto which it copied the (downloadable from Intel) EMC software and put it in a plastic bag next to the machine. I.e. - like so many things related to Linux - it is more of a kit, rather than a product.... So don't buy this for your grandmother.

Assembly instruction are MIA, downloadable from Intel, and even with that, it is a pain to get the drives in.

The one thing I miss from the current SS4200 'firmware' (it is really just a DOM flash, not EEPROM, so the naming is questionable) is support for S.M.A.R.T. monitoring.

EMC supposedly has a newer version of the software, but since they bought IOMega it is questionable if other boxmakers will get the new version from EMC or it will be IOMega exclusive. And I doubt that Intel will spend money on buying new software for a two years old product. On the upside, Intel just released the newest 1.1.... version of software only a few months ago, so there is hope.

The box has two PWM controlled (4 wires) fans and it can report CPU / MB temp and voltages, so the fans can be (and it looks they are) intelligently controlled. But w/o SMART support it does not report HDD temperatures. That is bad. (I suspect the HW is SMART capable, it is just the EMC distro.) Also since the design is about two years old, it uses a relatively old, high temp, high power consumption CPU. Performance wise it is probably similar to an ATOM, but it sure drinks more power.

The thing is highly hackable (hence geek-toy). You could take out the PATA DOM and put in a HDD for booting (it has been done), or just boot from one of the SATA drives. Looking back, you could get similar hardware together yourself and still not be far from the $150. Maybe even below. Would the EMC distro run on that? Would standby work on that? I don't know.

Using it is less time (to setup/configure) than building your Linux file server from scratch, but still more than just plugging in a WHS based box. On the other side WHS boxes are more expensive and they offer no RAID5, so you lose 50% of disk space to mirroring instead of 25% to parity. The SS4200 is pretty much the cheapest RAID5 solution you can buy as a box. WHS uses what I call 'file system level mirroring', so you can mix and match various size disks.

I think the best use for the SS4200 to populate it with 4 identical drives right from the beginning and not plan later upgrades. If you put in 2 drives it will create a mirror. If later you add another 2, you can not extend your disk space and 'upgrade' to RAID5 w/o destroying all the data on the existing 2 drives.

A downside to the RAID5 is that if your machine (PSU, CPU, whatever) fails, you can not 'just plug the drives into another box'. It is quite more involved than that. I am not even 100% sure you can get back your data, although probably yes. But not easily. Since the SS4200 uses pretty standard parts, you can probably replace many of them - at least temporarily - until you get your data off, but if the motherboard fails... say goodbye to your stuff.

BTW, I think that might be true for your data on the WHS boxes too. What can you do with those drives when (and not if) the box itself fails? I don't know.

So - as usual - RAID solutions are nice to handle HDD failures, but for data safety, backup is king. But if you do maintain (preferably offsite) backups, then the SS4200 is the cheapest and easiest way to get a RAID5 server with 75% of the disk space you purchased actually available for data.
Logged

JoeSchmuck

  • Level 3 Member
  • ***
  • Posts: 231
  • Retired Rocket Scientist
Re: RAID 1 rebuilds slowly
« Reply #12 on: December 22, 2009, 03:50:24 PM »

mzpx:

Now I like those numbers.  Maybe I'll look into a "Geek-Toy".  Yea, my NAS pulls 7 watts idle and 14 running, but to have a faster data transfer rate for the 35/90 watts, hummm....  So my mind is blank, actually I'm just tired, what is 50Mb/sec in MB/sec?

Wonder if I could run FreeNAS on that box.  It's a very full featured piece of free software.

Thanks for bringing up that box.

Also, I'm not sure how the drives are actually mirrored in the DNS-321 NAS.  I know mine took a long time to format it and about 5 hours to mirror ~600GB.  Well it was done in 5 hours, it could have been 3 because I just left it alone.

-Joe
Logged

mzpx

  • Level 2 Member
  • **
  • Posts: 25
Re: RAID 1 rebuilds slowly
« Reply #13 on: December 22, 2009, 08:56:39 PM »

@ JoeSchmuck about Intel SS4200:

I would not jump before looking.

- search for ss4200 and wiki. There is one with a list of description of hacks, alternative OS solutions, etc.;

- note that FreeNAS does not work flawlessly on this HW. No shutdown, etc. FreeNAS supposed to have support for SMART. That you gain over the EMC distro, but you lose some other stuff that comes from close integration with the HW;

-  OpenFiler was also installed, but installing is a pain as the box has no video out (!). It seem to me that OpenFiler does not support SMART monitoring. Also I doubt that the front leds would be controlled properly by OpenFiler. Again, gain some, lose some;

My point is that if you want to run FreeNAS or OpenFiler you might be better off getting some generic hardware, maybe check with the appropriate forums about compatibility before buying. For the same $150 you can get a cheap MB + CPU + Memory + case + PSU.

If you are not interested in the EMC distro this HW is not that great otherwise. Especially not in late 2009.

About performance (and other info):
(BTW, the SS4200 does NOT support jumbo frames, if you care for that.)

- read the review at smallnetbuilder.com;

- there is another review at tomshardware.com;

Both reviews (using the EMC distro) state that performance is great, but there are a few issues here and there. In general, what the software does not support - that won't happen.


BTW:

I just run into some issues with file permissions, etc. and just modifying the samba config does not work as it seems that the config file is created fresh from an XML config info on every boot. The DNS-321 sort of does that too, but there are workarounds (documented). So far I found no solution on the SS4200.


Summary:

I think the SS4200 (with the EMC software) is a nice solution for SOHO environment, can support a small group, has support for things like print server, ActiveDirectory, etc. It is also an intriguing alternative and an interesting toy for geeks. (That would be me.)

For most home users I believe the DNS-321 is plenty enough, it works fine as a basic file / media server. Even with the slow speed incremental backups are fine as long as you schedule them for night. And if you are a simple Windows users and can throw some more money on the problem, my recommendation would be a WHS box instead of a more elaborate Linux setup.

But as the cheapest RAID5 solution that you can buy w/o building your own, the SS4200 certainly have place in my heart.
(Even if I am not sure at this point if i would have been better off building a generic rig and putting OpenFiler on it.)
Logged

JoeSchmuck

  • Level 3 Member
  • ***
  • Posts: 231
  • Retired Rocket Scientist
Re: RAID 1 rebuilds slowly
« Reply #14 on: December 23, 2009, 06:42:44 AM »

Thanks for the info.  I will read up on it.

Yea, my next NAS will be something faster than the DNS-321.  The DNS-321 does everything I require, and more that I don't use so I can't complain at all.  The only thing I want on my next NAS is better throughput.  Maybe a nice low powered PC will be what I get or I could find a nice NAS box.  Until then I will read up on the Intel SS4200.
Logged