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Raid 1 Vs. Raid 0 EXCLUSIVE

The best way to think about both raid10 and raid0+1 is you take the last digit, in the case of raid 10 that is stripping and apply it to the first digit mirroring which makes it a stripe of a set of mirrors. Conversely you have with raid 0+1 you have a mirror of striped disks.

raid 1 vs. raid 0


I have a Dell power edge server 2u, with 4 SAS hard drives. I have installed perc 6i raid controller and now I want o configure raid 5 through Windows Server 2008 Disk management. If I install os on c and create raid 5 mirror with 3 hard drives as d on server, Will I be installing all the programs on dirve d the raid 5 mirror volume ? Any help

Hi I have IBM server and installed OS server 2012 r2. First time installing raid 1 configured but motherboard is changed so raid not configured. Is it possible raid configured without any problem and not create problem os and others. IBM server guide option raid configure with OS and raid only configuration.

While the above definition are 100% correct it is important to recognise RAID 10 is a relatively new term and there are many Raid 10 implementation out there that call them selves Raid 0+1. As late as 2006/7 manifacturers were documenting raid 10 implementations as raid 0+1

Dev Mgr, you miss the point of this discussion, if the Raid controller implements Raid 0+1 then it can not handle that failure mode if the raid controller implements Raid 10 then it can. It has nothing to do with level of intelligence of the controller or whether itis a low or high end controller, just the raid algorythm chosen. The selection of the latter has significant amounts to do with the level of intellience of the firmware developer but that said there can be good reasons to choose raid 0+1 over raid 10 !!!

Whether manual intervention as you describe will work really depends on the Raid software (frimware), what controls it allows and what meta data it stores, do not assume the raid software will allow such activity.

Hi Leon, your maths fails to take into account that in raid 0+1 after the first failure half the disks are no longer available (in the above example two good disks will have effectively been failed along with the bad disk).

In raid 0+1 the first disk failure fails all disks in that stripe, the failure of any subsequent disk means a member of the other stripe has failed and so data access is lost. Two disk failures = total data access losss

Secondly the idea of re-constituting the data from the surviving drives may not work as some raid implementations will not allow such and action as they track the membership using meta-data store either on the drive or in the controller.

In raid 10 you have 4 hard drives seperated into 2 groups of hard drives . Group 1 contains drive 1 and drive 2. Drive 1 contains letters a and b which it reads at 1 letter per second. Drive 2 is a copy of this so it also reads at 1 letter per second, however these speeds do not add together to read a and b at 2 letters per second, drive 2 is more like a backup. This means letters a and b take 2 seconds to be read. At the same time group 2 (containing drives 3 and 4) reads letters c and d. Drive 3 reads letters c and d at 1 letter per second, and drive 4 is identicle and a sort of backup. This means letters a and b are read in two seconds and because this is done at the same time as group 1 reads a and b (read In 2 seconds) letters a,b,c and d are al read in 2 seconds. 2x faster than one hard drive.

The main difference are that in raid 10 drives 1 and 3 could both fail and the system would still run because drives 2 and 4 would take over. This means that drives 1 and 3, 1 and 4, 2 and 3 or 2 and 4 could both be down, but the system would still be running as the two functional drives would take over. Whereas in raid 01 if drive 1 or 2 failed group one would fail and group 2 would take over. This means drives 1,2,3 or 4 could fail and the system would still be functional, but if anymore failed the system would fail.

On raid 10, each mirror set is 2 of the same drive, and your controller can and will use them interchangeably. Disks 1, 4 and 5 could all fail, and the raid would run. You could pop in new drives, and it would repopulate.

On raid 01, the mirroring is /after/ the striping. You have 2 striped sets. When one drive fails in a striped set, the whole set is shit. Your controller cannot substitute disk 2 for 5 in a raid 01. If disk one and five both fail, the raid is toast.

What will be the 3-disks raid 01 configuration? (as mentioned above).>> It requires minimum of 3 disks.And by the way, raid 10 can be built with 2 disk only (mdadm can do it). It will write as Raid 1 and read as raid 0.

The last three fields on this line are the file system mount options, the dump frequency of the file system, and the order of file system checks done at boot time. If you don't know what these values should be, then use the values in the example below for them (defaults,nofail 0 2). For more information about /etc/fstab entries, see the fstab manual page (by entering man fstab on the command line). For example, to mount the ext4 file system on the device with the label MY_RAID at the mount point /mnt/raid, add the following entry to /etc/fstab.

I see the description here but it explains by dividing disks into groups and one disk if fails in each group there is no data loss in raid 10 but there can be data loss in raid 01. But what do these groups physically mean? Aren't there basically just 6 disks in the example in the given link?

I see this link -32-raid-raid0-raid10-explained#.where the discussion ends concluding that in case of RAID 01 if any disk fails in one of the array/group consisting of stripes, all the disks become inaccessible by the controller. But for RAID 10 the controller can access the good disks of the array/group consisting of mirrored disks. Why is it so? When there is a read/write request why can't in case of RAID 01 it just access the good drives in array/group 1 and the drive which failed be accessed into the other group/array which is the mirror of group/array1?

Raid 1. Great read speed only if driver properly implemented - If you use Areca and LSI raid controllers, they can deliver almost the same read capability for Raid 1 sets as Raid 0 sets (within 10%). Note that for software raid solutions there are two types, OS-software and Motherboard-software.

Raid 5. a very mixed bag: for sequential reads, it is faster than raid 1/0, and for random read it is slightly slower that that. Note that the performance of raid 5 is very dependent on the speed of the controller (e.g. you can't expect much in onboard raid).

Raid 6. Redundancy increased compared with Raid 5. two drive can fail at anytime, and when rebuilding the array after 1 drive failed there is still redundancy (note that when raid 5 drive failed, the array is similar to raid 0 - any drive fail = total loss).

If you purchase a hardware raid controller go with RAID5. It has the least overhead and the hardware raid controller will almost eliminate the write overhead penalty since it calculates the parity bits in hardware. Raid5 also reads off multiple disks simultaniously improving read and write speed.

Microsoft recommeneds raid 10 for SQL server. but before taking about raid 10 I would like to mention going to RAID 0 for SQL server too risky because if a drive failed in RAID 0 your data will be lost the only way to recover it to use a privous backup file. I would like to recommend you to change RAID configuration as soon as possible.

With 20 2Tb SATA desktop/consumer drive, you would almost be guaranteed of at least 1 unrecoverable read error during rebuild. So with any single parity raid setup, you are going to technically loose data, with no warnings.

An ZFS raid consists of several groups of disks. Each group needs full redundancy, thus each group should be a raidz1 (raid5) or raidz2 (raid6) or raidz3 or mirror. Thus, collect several raidz1/raidz2/raidz3/mirror into one ZFS raid.

Also, one group of disks gives the IOPS of one single disk. If you have one raidz3 in your ZFS raid, then you have the IOPS of one disk. If have two groups in your ZFS raid, then you have the IOPS of two disks. etc. This is the reason you should never use one single raidz3 spanning 20 disks. You will get very bad IOPS performance.

It is recommended to use several groups in a ZFS raid. Each group should consist of 5-12 disks depending on the configuration of each group. A raidz3 group should use 9-12 disks. A raidz2 group should use 8 disks or so. 041b061a72


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