Document fins/I0635-1
FIN #: I0635-1
SYNOPSIS: Sun StorEdge T3/T3+ Array volumes configured as RAID 1 cannot
reliably withstand multiple drive failures
DATE: May/14/01
KEYWORDS: Sun StorEdge T3/T3+ Array volumes configured as RAID 1 cannot
reliably withstand multiple drive failures
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- Sun Proprietary/Confidential: Internal Use Only -
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FIELD INFORMATION NOTICE
(For Authorized Distribution by SunService)
SYNOPSIS: Sun StorEdge T3/T3+ Array volumes configured as RAID 1 cannot
reliably withstand multiple drive failures.
TOP FIN/FCO REPORT: No
PRODUCT_REFERENCE: T3/T3+ Array RAID 1+0
PRODUCT CATEGORY: Storage / Service
PRODUCTS AFFECTED:
Mkt_ID Platform Model Description Serial Number
------ -------- ----- ----------- -------------
Systems Affected
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- Anysys - System Platform Independent -
Mkt_ID Platform Model Description Serial Number
------ -------- ----- ----------- -------------
X-Options Affected
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- T3 ALL StorEdge T3 Array -
- T3+ ALL StorEdge T3+ Array -
PART NUMBERS AFFECTED:
Part Number Description Model
----------- ----------- -----
- - -
REFERENCES:
BugId: 4374724: Multiple Non-Adjacent Disk Failures in a RAID 1 stripe
causes LUN to unmount.
4377484: dual drive failure in RAID 1 w/standby kills LUN.
PatchId: 
109115 - T3 1.18.00: System Firmware Update.
112276 - T3+ 2.00.01: System Firmware Update.
SunAlert: 26177
PROBLEM DESCRIPTION:
Customers with Sun StorEdge T3/T3+ Arrays configured with RAID 1 volumes
may expect these volumes to be resilient to multiple non-adjacent disk
failures. However, multiple non-adjacent disk failures can still cause
data inaccessibility. All the customers who configure RAID 1 LUNs and
expect to survive multiple non-adjacent drive failures on those LUNs
could experience this problem. Customers may become dissatisfied
because a feature they believe they paid for (RAID 1+0) does not work
as advertised.
Currently, the StorEdge T3/T3+ Array has RAID 1 capability. This
capability is marketed as RAID 1+0 and described as RAID 1+0 in the
user documentation. This generally implies the system is resilient to
multiple drive failures, as long as two drives containing both the
primary and mirror of any data stripe are not lost. Due to the
T3/T3+'s design and T3/T3+ firmware bugs, RAID 1+0 is not actually
delivered by the T3/T3+ array.
When volumes are configured on the Sun StorEdge T3/T3+ Array using
hardware RAID 1, data is striped and mirrored on the selected drives
configured for use in that volume. Mirroring of each stripe is
performed on the adjacent drive(s). This is commonly referred to as
RAID 1+0, as mirroring occurs at the stripe, or column level. If two
adjacent disks fail, the volume will unmount because there is no valid
data available. This is a generally known and accepted behavior of the
T3/T3+, given the design. However, if two non-adjacent drives fail,
the volume can still unmount, making data inaccessible. This is not
consistent with accepted RAID 1+0 behavior. As long as a valid copy of
data exists on the remaining drives following a multiple drive failure,
the data should remain available and the volume should stay mounted.
Currently, the volume configuration facility can only record one
disabled disk per volume. Many changes to the T3/T3+ firmware are
required to make RAID 1 volumes resilient to multiple non-adjacent disk
failures.
Until the behavior is fixed with a firmware change, customers
configured with RAID 1 LUNs should be made aware of the limitations of
the array under a multiple drive failure condition. Customers
selecting RAID 1 to achieve higher levels of availability over RAID 5
should be informed that the level of availability delivered for these
configurations is the same, i.e. neither can reliably withstand more
than one drive failure and still keep data online.
IMPLEMENTATION:
---
| | MANDATORY (Fully Pro-Active)
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| | CONTROLLED PRO-ACTIVE (per Sun Geo Plan)
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| X | REACTIVE (As Required)
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CORRECTIVE ACTION:
An Authorized Enterprise Field Service Representative may avoid the
above mentioned problems by following the recommendations as shown
below.
This problem is now fixed with the following firmware releases.
Please obtain following patches and install as directed:
. If Sun StorEdge T3 with FW 1.18 and above, install patch 109115
or later.
. If Sun StorEdge T3+ with FW 2.0.1 and above, install patch 112276
or later.
. If Sun StorEdge T3 with below FW 1.18, or, Sun StorEdge T3+ with
below FW 2.0.1, then perform the following workaround:
Do not select RAID 1 over RAID 5 if required for availability
reasons. If RAID 1+0 is a requirement for data availability, it
should be done using host-based software, e.g. Solstice DiskSuite
or Veritas Volume Manager.
Certain workloads, e.g. small random writes can benefit from using
RAID 1 over RAID 5 and should still be used in those environments
if performance is a concern.
COMMENTS:
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Implementation Footnote:
i) In case of MANDATORY FINs, Enterprise Services will attempt to
contact all affected customers to recommend implementation of
the FIN.
ii) For CONTROLLED PROACTIVE FINs, Enterprise Services mission critical
support teams will recommend implementation of the FIN (to their
respective accounts), at the convenience of the customer.
iii) For REACTIVE FINs, Enterprise Services will implement the FIN as the
need arises.
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