Dell PS4000 - RAID 6 Implementation Details; EqualLogic Volumes Overview

Dell EqualLogic Configuration Guide v11.3
10
Disk Drive
Qty / Size
50
(a)
100
(a)
74
146
250
300
400
450
500
600
750
1000
2000
7
(b)
-
-
-
-
1250
-
-
-
-
-
-
-
-
8
(c)
-
-
-
-
1500
-
-
-
-
-
-
-
-
14
(d)
-
-
888
-
3000
-
4800
-
6000
-
-
-
-
16
700
1400
-
2044
3500
4200
5600
6300
7000
8400
10500
14000
-
48
-
-
-
-
-
-
-
-
21000
25200
-
42000
84000
(a) Solid State Disk
(b) Legacy PS50E
(c) PS4000E and PS6000E only
(d) Legacy PS70E,PS100E, PS100X, PS200E and PS300E
Table 6: RAID 5 Total Storage Available with Hot Spares (in GB)
2.4.2 RAID 6
RAID6 (striped set with dual distributed parity) combines N disks in an arrangement where each stripe
consists of N-2 disks that contains data blocks and 2 disks that contain parity blocks. Each parity block
generates parity using a different ―view‖ of the data blocks depending on the RAID 6 implementation.
RAID 6 implementations can tolerate up to 2 drive failures per RAID set at the same time without data
loss. RAID 6 is not recommended for workloads consisting mainly of random writes. For EqualLogic
arrays using a RAID 6 policy, Table 7 shows the drive layouts that are enforced based on the number of
drives in each array and the hot spare configuration.
Disk Drives
Hot Spare
No Hot Spare
7
6 Data/Parity
1 Hot-spare
7 Data/Parity
8
7 Data/Parity
1 Hot-spare
8 Data/Parity
14
13 Data/Parity
1 Hot-spare
14 Data/Parity
16
15 Data/Parity
1 Hot-spare
16 Data/Parity
8 / 8
(c)
13 Data/Parity
(d)
1 Hot-spare
16 Data/Parity
48
(a)
47 Data/Parity
1 Hot-spare
N/A
(b)
(a) 48 drive arrays implement multiple RAID 6 sets within a single chassis.
(b) 48 drive arrays cannot implement a no hot-spare RAID policy.
(c) PS60x0 XVS with 8x 100GB SSD and 8x 450GB SAS.
(d) One 450Gb hot spare, 2x 450 Gb parity and 2x 100Gb SSD parity.
Table 7: RAID 6 Drive Layouts
Table 8 shows the amount of raw storage available using the hot spare drive layouts specified in Table
7 above.