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RAID Confusion on ReadNAS 628X
I currently have 5 of my 8 drive bays all filled with identical HDDs. They are configured in "X-RAID". I have two questions:
1. What is the difference, if any, between X-RAID and RAID 5?
2....
Hi XrayDoc88,
1. What is the difference, if any, between X-RAID and RAID 5?
X-RAID is the auto-expandable RAID technology that is available only on ReadyNAS systems. It uses the standard RAID levels, RAID 1, 5 and 6.
With two disks, it will use RAID-1. With three disks, it will use RAID-5. With 4 or more disks, you can optionally select X-RAID with dual redundancy(RAID-6).
With X-RAID, you can add storage space without reformatting the drives or moving the data from another location. You may check this link for more information about X-RAID.
2. I currently get 4 x my drive size as usuable storage space. If I add a sixth HDD, will I get 5 x my drive size as usuable space, or will the NAS automatically convert to RAID 6?
If the volume is configured with X-RAID with single redundancy (RAID-5), it will not automatically convert to RAID-6 when you add the 6th drive. Changing to X-RAID with dual redundancy (RAID-6) would require you to destroy and recreate the volume.
Regards,
Thank you for the clear explanation!
Unless something has changed in recent OS versions, adding a 7th drive will convert to RAID6 unless you first switch out of XRAID.
Sandshark wrote:
Unless something has changed in recent OS versions, adding a 7th drive will convert to RAID6 unless you first switch out of XRAID.
Are you saying that the volume would change automatically to RAID 6 without data loss? Or would you be forced to create a new RAID 6 volume?
I've always wondered what the maximum number of HDDs are that could be configured in RAID 5. You must be saying it is 6? Clearly you couldn't build a RAID 5 array with 15 HDDs and only a single HDD used for redundancy.
XrayDoc88 wrote:
Sandshark wrote:
Unless something has changed in recent OS versions, adding a 7th drive will convert to RAID6 unless you first switch out of XRAID.
Are you saying that the volume would change automatically to RAID 6 without data loss?
Yes (which also means there would be no increase in capacity). Note this does assume that the biggest three disks in the RAID-5 array are the same size.
XrayDoc88 wrote:I've always wondered what the maximum number of HDDs are that could be configured in RAID 5. You must be saying it is 6? Clearly you couldn't build a RAID 5 array with 15 HDDs and only a single HDD used for redundancy.
There is no maximum, and in fact you can build a RAID-5 volume with 15 HDDs. I'm not saying that's a good idea, but it is possible. Netgear simply decided (somewhat arbitrarily) to have XRAID transitition to dual redundancy when the 7th disk was added in a desktop NAS. My recollection is that the rackmount models switch to dual redundancy when the 6th disk is added.
One clarification - with RAID-5 the parity blocks are not stored on one disk. They are distributed evenly across all the disks. That improves write performance, and also balances the disk I/O evenly across all the disks.
One clarification - with RAID-5 the parity blocks are not stored on one disk. They are distributed evenly across all the disks. That improves write performance, and also balances the disk I/O evenly across all the disks.
Well I didn't know that fact. I also didn't know that in theory there is no maximum number of HDDs in a RAID 5 array. So with that understanding (just for fun) can the total usable space of a RAID 5 array truly always remain at total number of discs minus 1? It seems to me that if your number of discs got high enough, say 100, that the amount of distributed parity data must eventually equal more than a single disc size.
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