RAID Data Recovery & Server Recovery
A server usually refers to a network attached computer system designed to process requests and deliver data to other computers attached to the network. If you're in business today, you likely have at least one server that is critical to operations. Whether it's a file server, an email server, an application server, or your web server, if it goes down, we know it can be catastrophic. We understand time is money and it can't wait. But the steps you take immediately following the discovery could be the most important steps you ever take! What do we advise? Well if it really is absolutely critical... DO ABSOLUTELY NOTHING! More data is permanently lost from well intentioned attempts to resolve the issue "in- house", than is ever lost as a result of the initial problem. If you can't live without it, use a professional data recovery service... period!
Because servers needed to quickly access and store large amounts of data safely, RAID was developed. The term RAID stands for Redundant Array of Independent (or Inexpensive) Drives. RAID 5 is by far the most popular form in use, and the flavor of RAID we are discussing in general. As the name implies, RAID is a method of joining multiple hard drives together to form one large very fast virtual disk drive AND it's designed so if any one hard drive fails, the integrity of the data will remain intact. This is accomplished by using one drive or stripe, for parity. Here is a simple illustration of how it works showing the truth table for 2 bits of data and the corresponding parity bits (yes it's a simple exclusive OR gate for you geeks out there). It shows what the parity bit would be for each unique combination of data bits. Parity is 0 if the two data bits are the same. Parity is 1 if the two data bits are not the same.
|Data bit 1||Data bit 2||Parity bit|
For example, let us say that data bit 2 was unreadable, but you know that data bit 1 is a 0 and the parity bit is a 1. Using the table we can see that the unreadable bit 2 must have been a 1. This simple but effective method is the same technique used in RAID but on a much larger scale.
RAID configurations are found in a lot of products that you would not expect; including some low end consumer products. For instance, it has been quite common for manufactures to combine two 500GB hard drives in a RAID 0 configuration to create a 1TB external USB box.
RAID configurations are found inside most NAS or Network Attached Storage boxes as well as within SAN or Storage Attached Networks. In fact, SAN has been described as simply a RAID with a Fibre-Channel network connection while NAS has been described as a RAID with an Ethernet network connection.
As mentioned earlier, there are many different levels of RAID and below is a brief description of each.
- RAID Level 0 – Data is striped in set block sizes across multiple hard drives with no parity. Access speed is increased over a single disk drive, but this is
not really a RAID in our opinion as there is no redundancy or built in method of recovering the data if a single drive fails. RAID 0 is mainly used for joining 2 smaller drives to appear as 1 larger drive.
- RAID Level 1 – Each data drive is being simultaneously mirrored to another data drive ensuring an exact image is always available. This provides redundancy and faster speeds when reading
data, but requires double the storage volume.
- RAID Level 2 – Data is striped at the bit level and uses ECC type correction methods for recreating lost data.
- RAID Level 3- Data is striped in bytes across multiple drives with one dedicated parity drive. It is seldom used.
- RAID Level 4 – Data is striped in set block sizes across multiple drives with one dedicated parity drive. This method is quite common but the need to constantly update the
one dedicated parity drive can become a bottleneck.
- RAID Level 5 – Data is striped in set block sizes across multiple drives with distributed parity (parity distributed equally across all drives in the array). By providing an
excellent blend of speed, safety and capacity, RAID 5 has become the most implemented format of RAID today.
- RAID Level 6 – Very similar to RAID 5 but uses two parity drives which allows the recovery from the simultaneous failure of two hard drives. Access speed is diminished somewhat. This format is rare.
- RAID Level 7 - An improved version of RAID using a dedicated parity drive similar to RAID levels 3 or 4 BUT with caching to get around the bottleneck created by dedicated parity
drives. This particular RAID level is proprietary to Storage Computer Corporation and is not an industry standard.
- Nested RAID Level 0+1 or 01 – Fittingly referred to as a Mirror of Stripes, this is basically a RAID 1 implemented with two RAID 0 striped sets (instead of 2 actual hard drives).
Simply said, the RAID keeps an exact copy of a striped set.
- Nested RAID Level 1+0 or 10 – Similar as above but reversed in which RAID level is the 1st building block, this Stripe of Mirrors is a RAID 0 or striped set implemented across mirrored RAID 1 sets of drives.
- Reasons for Data Loss on RAID, NAS, SAN and Servers
- How We Recover Data from Servers, RAIDS, SAN & NAS
- Supported Manufactures of RAIDs & Servers
Losing access to the data on your RAID array can happen for a number of reasons. However there are two distinct categories of data loss that will require RAID data recovery services.
- LOGICAL OR SOFTWARE ISSUES - All of the hard disk drives that make up the RAID array are functioning properly. The RAID data cannot be accessed because of damage to the file system. The operating system whether Linux, MAC or Windows, uses the file system to locate the data on the RAID array. One can think of the file system as a large index containing the location and order of all the parts of data that make up a particular file. Examples of file system damage on RAID arrays include:
Accidental deletion Incomplete Rebuild RAID initialized reformatted Accidental Format or FDISK Malfunctioning controller RAID missing drives Array incomplete Master Boot Record bad RAID Parity error Blue Screen of Death MFT Master File Table damage RAID rebuild error Created New Volumes Missing RAID partition Use of Chkdsk or Utilities Improper shutdown Power Interruption Surge Re-configured RAID RAID configuration error NTLDR is missing RAID configuration lost Replaced wrong drive Virus Infection Volume Reconstruction Error
- PHYSICAL ISSUES - One or more of the hard drives in your server, RAID box, SAN or NAS are NOT functioning properly. RAID5 is created to allow the failure of one hard drive with no loss of data. However, the failure of one drive can cause the RAID to start rebuilding itself and if another hard drive in the array fails even momentarily during this process, data can become inaccessible. Hard disk drives may become defective for a variety of reasons as outlined in the hard disk drive recovery section.
RAID Data Recovery from a single drive server or a multiple drive RAID 5 array is initially treated much like any other recovery. Memofix's first step is to secure exact images or mirrors of all the storage devices. We may need to repair a defective or crashing hard drive in order to get an image. If it is a single hard drive we would then use our standard analysis and RAID data recovery techniques to repair any logical damage. In most cases we do not have, nor need your RAID box or controller. Once images have been secured, we analyze the entire set of RAID drives to determine the original stripe size, block size, and striping scheme. By calculating and scanning the parity across the entire RAID array we can identify the integrity or degradation of any RAID stripe or slice. We then assess any damage in relation to the original installation and attempt to segregate or repair the effects of that damage. Then using specialized RAID utilities, we attempt to mount the RAID volumes virtually and repair any damaged file system structures that may be preventing us from accessing the data. In other cases where the damage is more severe we may choose to de-stripe the RAID to another storage device. Either way, Memofix should then be able to access the damaged volumes and use our standard recovery techniques to salvage the data.
- In the cases of a multiple drive RAID array with parity or redundancy built in, there is another option available if one of the drives becomes inaccessible or corrupted. We can simply use the data from the remaining good drives to recreate the data off the one inaccessible drive. However, a good RAID implementation should have already informed you of any drive failure and seamlessly continued to operate by recreating the missing data on the fly. In most instance RAIDs we see for recovery are in much worse shape.
- We see cases where one drive of the RAID array failed 4 months previous. The defective hard drive was NOT replaced and the RAID continued to operate in a degraded mode until a 2nd hard disk failed. At this point the RAID now has 2 bad drives which render it totally inaccessible.
- We also see a lot of RAID cases where a single disk drive failed and the operator installed a new drive in its place and rebuilt the array from scratch.
- Or we see RAIDs where a new drive was installed in the wrong slot and when the RAID attempted to rebuild, it corrupted itself.
We see such an enormous variety of damage that was caused after the initial failure and by the user's recovery attempts, that we must stress the same advice, time after time; if your data is life and death, do nothing after discovering a data loss and send it to the RAID data recovery specialists!
|2Degrees Frost Data Solutions||Concurrent Computer||IBM||Omneon Video Networks||Storage Computer|
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|Accordance||Crossroads Systems||Index Engines||Panasas||StoreAge|
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|Archion||Digi-Data||JMR Electronics||Quantum||Terrascale Technologies|
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|Arena MaxTronic||DISC||Kano Technologies||RAID||Thecus|
|ARIO Data Networks||DiskSites||Kazeon Systems||RAID King||Themis|
|Aristos Logic||D-Link||LaCie||RAIDION Systems||Thinking SAFE|
|ASACA||Dot Hill||LAND-5||RARE Systems||Third I/O|
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|Brocade||Excel/Meridian Data||NetCom USA||SANRAD||Wasabi Systems|
|Buffalo Technology||FalconStor Software||NetConvergence||Sans Digital||Weibtech|
|Bus-Tech||Fantom Drives||NetEngine||Seagate||Westek Technology|
|Caen Engineering||FCIA||NETGEAR||SEEK Systems||Western Scientific|
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