Tag Archives: RAID

Which RAID Settings Should I Use For My NAS?

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RAID 1 (Mirror)

A NAS (Network Attached Storage) puts storage onto your network, where it can be accessed by many computers. They often have more than one hard drive which can allow you to have automated copies of your data, which is known as RAID. A common type of RAID found on NAS devices is RAID 1, which will make two hard drives into a mirror copy of one another. Some manufacturers call RAID 1 Safe mode. If you have a NAS with two 1TB hard drives and set them to RAID 1 mirroring, instead of 2TB of storage (1TB x2) you only get 1TB. Everything you store to the NAS gets saved to both drives automatically. The theory is that if one of the drives fail, you can access all of the data from the other one. In practice that is not always the case. More on that later.

RAID 1 Mirror Animation

RAID 1 Mirror Animation

RAID 0 (Stripe)

Another common NAS option is RAID 0. The “R” in RAID stands for redundant, however there is no redundancy in RAID 0, so it’s not a real RAID type. If you setup the same two 1TB disks as RAID 0, you will get a 2TB volume to store your data on. The problem is that every single file you write to the NAS will be split into tiny pieces and distributed across both drives. If one drive fails, you not only lose the data from that failed drive, but also from the non-failed drive as it only contains half the pieces of each file. RAID 0 should never be used for long term storage, but can be fast so is often used for video editing.

RAID 0 Stripe

RAID 0 Stripe

So that’s the hardware taken care of. What other things should you look out for when choosing a NAS?

Another problem with most NAS devices is the non-standard filesystems they use to store the data on the disks. If the NAS itself fails, you cannot usually read the disks by attaching them to a standard PC. So even in RAID 1 mirror mode, you could end up with no usable copies of your data. Most NAS drives run a simplified version of Linux, but only some of them use standard Linux filesystems like ext2/3/4.

Backup my backup?

Some NAS drives have a USB port to allow you to backup the data to an external hard drive. This is great, as long as you can access the backup data on a regular PC, and it doesn’t need to go through the NAS. You can imagine why that would be a problem.

To summarise, NAS drives can be a great way to upgrade your home or small office storage. They can allow collaboration and sharing of files between users, and should simplify your backup process. Just remember that a NAS is a small server that needs to be backed up as a matter of urgency. As long as you have that covered then a NAS can be a smart addition to your network.

How a Data Recovery Engineer Sees RAID

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As somebody recovering data from RAID arrays, my view on them is a little different to the norm. In most cases I would say avoid RAID wherever possible. Simplicity is key.

Below are my answers to some real questions I have received from clients about RAIDs.

Why did this RAID disk fail?

Hard drive failure is not unusual and is often not avoidable. The truth is that all hard drives fail eventually, whether they are used in a RAID or not. Even though a RAID system can provide some fault tolerance from physical drive failure, they do have limits. A RAID5 on three disks for example can only handle a single drive failure at any one time. It is common for a second disk to fail whilst the other disk is being replaced. This is when RAID recovery is required; to first access the failed drives, and then rebuild the RAID. The best protection against RAID failure is to make backups. Backups in as many formats, in as many different physical locations as possible.

Why did the server fail so badly? Isn’t RAID meant to prevent this?

A 3-disk RAID5 can only cope with one bad disk. This doesn’t help when two drives fail at the same time. Although a RAID array can provide some leeway when it comes to disk failures, it doesn’t always help when you have multiple failures in quick succession. Adding more disks to the RAID can provide more redundancy, however this costs more money, and also adds complexity when things go wrong. Also you could be in a similar position if three disks happen to fail next time. A live system could fail at any time so prepare for the worst. Backups are cheap, and take a relatively short amount of time. RAID recovery can be expensive and cause unnecessary downtime.

Why couldn’t our IT support recover this?

We are a specialist data recovery company, with access to tools and resources which are not available to IT Support staff. We have spent the last fifteen years perfecting the process of extracting data from failed & failing hard drives and RAID arrays. For the best chance of recovery, we like to get the drives as soon after failure as possible. If more work gets carried out on the drives, things can be made much worse.

How can we avoid this happening again in the future?

To avoid similar problems in the future, the best way forward is some form of regular backup. The backups should be verified and then tested / restored as often as possible. This is where disaster recovery comes in, which can involve simulating certain types of failure and making sure you can get up and running again from your backups. At the very least, it wouldn’t hurt to put the really crucial business files onto an external hard drive every few weeks and store it in your company safe. It’s low-tech but at least you could plug it in to any PC and access the important business data if required as a last resort.

I’m not against RAIDs. They do have their place, but cannot be relied upon as a replacement for regular backups.

We have more articles about RAID here.

Novatech Data Recovery Nationwide

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Following the success of our local data recovery partnership with Novatech, we now have expanded our partnership services to cover Novatech’s other stores nationally. You will find our leaflets at the service department counter in your local store.

Why RAID Can Be Bad For Business

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RAID is often touted as the silver bullet in data storage. Increased storage capacity, resistance from hardware failures and improved performance. While these are all valid upsides to a RAID setup, there are also a few downsides which need to be addressed.

1. Extra Storage.

RAID can allow for a huge pool of storage, but with that storage comes great responsibility. You should factor in at least enough capacity to backup the RAID data somewhere else. If you can only afford 8TB of storage then you should only use 4TB for data and the other 4TB to back it up; Preferably on another machine / standalone system.

2. Redundancy.

The first letter in RAID stands for redundancy. This means you can afford to lose a certain number of disks without losing access to your data.  This also means that if you have a disk failure you need to get it replaced immediately, otherwise you’re running without redundancy.

3. Downtime.

Nobody likes downtime. If your 16TB RAID array goes offline without a backup then you have a couple of options. One option is to attempt to get the RAID back online by replacing disks, rebuilding the array etc, but this is risky. If this is your only copy of the data then rebuilding / reformatting the RAID could corrupt the data beyond recovery. Don’t do this if you don’t have a backup to fall back on.

The second and preferable option is to get the RAID professionally recovered. When we receive a RAID, the first thing we do is make images of all disks. This allows us to work on the RAID without risk. Then we use a read-only process to extract the data onto another form of storage. This is where downtime comes in. Unless you go for an emergency process, you could have to make do without the data for a number of days.

So What’s The Way Forward?

It’s one word. Redundancy.

Whatever you do, make sure your data is replicated across as many types of storage as possible. In an ideal world you would have a duplicate system running alongside the live system, which can take over if anything goes wrong. Then have the data on another type of storage, which you can access from somewhere else. Imagine if the RAID controller failed, and you could only access the data from that one machine.

It doesn’t matter how many backups you have if they all require the same system to access them.

I’ve only just scratched the surface here, but you should always look to make extra copies of your data. It may seem redundant now, but when your server fails containing all your data, all your accounts, all your client details and your website, you’ll be glad you kept that extra copy.

ST373454LC Unusual RAID drives

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ST373454LC Unusual RAID Drive

ST373454LC Unusual RAID Drive

We have recently recovered a RAID 5 array which consisted of three of these ST373454LC SCSI hard drives. These are solid, weighty drives, which don’t give off a great deal of vibration, despite spinning at 15,000 rpm; 3 times faster than most laptop hard drives!

Upon opening one of the drives for cleanroom rework we discovered why these drives  spin so quietly. In the picture below you can see that although the drives are standard 3.5″ form factor, they actually have 2.5″ disk platters. These smaller disks create less drag, and therefore can spin faster without stability problems.

Inside a ST373454LC Hard Drive

Inside a ST373454LC Hard Drive

These drives are not alone in mixing up the form factors. The popular WD Raptor drives also use a similar design.

Downside?

Of course the biggest downside to using smaller disks is the lower storage capacity. Typically SCSI hard drives are much lower capacity than their SATA counterparts, so this trade-off is acceptable for the speed and reliability increases. The relatively low capacity is further mitigated when the drives are used in RAID arrays.

RAID 5 HP Smart Array E200i Recovered

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Smart Array E200i SaS Drive

HP Smart Array E200i SaS Drive

We have just competed a successful recovery from an HP Smart Array E200i RAID array. Not a standard case this. It had x3 DG146BB976 2.5″ SaS drives, two of which had been overwritten with a new RAID 1 mirror.

We found the disk order which was not the same as the labelled numbers. This is often the case. Also, due to the rebuild that had occurred we had to drop one of the disks and virtually rebuild it using the parity information from the other disks.

3 DG146BB976 SaS ST9146802SS Drives

3 DG146BB976 / ST9146802SS SaS Drives

4K Sectors & RAID

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ZDNet has an interesting article about 4K sectors (Advanced Format), however what was more interesting was the bit about large SATA drives.

 Today’s large SATA drives shouldn’t be used in 4 drive RAID 5 arrays due to the high likelihood of a read error after a drive failure, which will abort the RAID rebuild.

It is a common misconception that if you run a RAID system then you can avoid keeping backups. Although fault tolerant to a point, there are plenty of issues with RAIDs that can at best cause lengthy downtime and at worst prevent any recovery at all.

More info on RAID Recovery

Apple & Lacie Thunderbolt Technology

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Apple officially unveiled the newly updated MacBook Pro range featuring new high-speed Thunderbolt I/O technology and improved processor and graphics offerings back in February 2011. LACIE have just announced the Little Big Disk with Thunderbolt Technology to support this range of Macs. Running on PCI Express and DisplayPort protocols, data transfer speeds between peripherals on Thunderbolt technology can reportedly be done 20 times faster than USB 2.0. LACIE also mention the use of SSD technology in the little big disk to complement this technology, using two 250GB Intel 510® Series Solid-State Drives (SSD). The two solid-state drives are preconfigured as a Striped RAID Set for enhanced performance.
Our only concern with SSD technology is it’s reliability and endurance.
As with any non-volatile floating gate memory device, the more you cycle the device the more failures you tend to observe, and the less data retention you get. So although the I/O technology is the way forward, the type of device used for critical data storage, is still a question to be answered.

LaCie 5Big RAID 6 Recovery

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I will start by saying that we can, and have, recovered data from these drives. As with all RAID recovery we carry out, we never use the original controller or drives to access the data. We image the drives on an individual basis and then work on these drives to rebuild the RAID using a form of RAID emulation. The most time consuming part of this type of recovery s determining the proprietary RAID settings that the manufacturer has used.

Due to the complex nature of these NAS devices, we always recommend they are backed up to another form of media. Although recovery is possible, it can be expensive and relatively time consuming. Also if the unit is powered on and rebuilds are attempted then the recovery can be made more complicated or even impossible.

A Little Background

The LaCie 5Big NAS device contains five hard drives and allows for a number of different configurations. One of these configurations is RAID 6, which works in much the same way as RAID 5, but with an additional parity stripe. This additional parity stripe uses an algorithm which requires a relatively high processing overhead, so RAID 6 has rarely been seen in consumer level devices. The low cost of processing means that RAID 6 is now a viable option for embedded NAS devices such as the LaCie 5Big.

The advantage of RAID 6 over RAID 5 is that with 5 disks it can theoretically cope with two disk failures. This gets round an increasingly common problem with large capacity RAID 5 arrays where if a second disk fails whilst rebuilding a failed disk, there should be enough parity information to continue the rebuild successfully.

If you have a failed or broken LaCie 5Big then use the contact details on the right to contact us. Alternatively you can leave a comment here and we will get back to you.