Splunk to Microsoft Sentinel SIEM Migration
Splunk to Microsoft Sentinel SIEM Migration moves your detections, data sources, and day-to-day security operations from Splunk — Enterprise, Cloud, or Enterprise Security — onto Microsoft Sentinel, beginning with a fixed three-week window quoted per estate. In that window IT Partner inventories every Splunk input and saved search that actually matters and records a disposition for each, maps every source to a Sentinel connector, converts an agreed initial set of SPL detections to KQL analytics rules (Microsoft's SIEM migration experience where it translates cleanly, engineers where it does not), brings Sentinel live beside Splunk on those sources with a first incident-parity reading, and hands over the cutover runbook, the decommission checklist, and a cost model built from your measured ingest — commitment tiers versus pay-as-you-go versus your Splunk renewal — with the assumptions written down. The full parallel run, the remaining sources and detections, and cutover with Splunk standing as the rollback are quoted from that inventory as an extension — a number built on measured facts, not a guess. Running the SOC after cutover is a separate service; this page is the migration.
What this engagement is
Most Splunk-to-Sentinel conversations start with a renewal quote and end with a question about telemetry. If your estate already runs Microsoft 365, Entra ID, Defender for Endpoint, and Azure, a large share of the security signal you pay Splunk to ingest is generated by Microsoft products with native Sentinel connectors — several of those sources ingest at no charge, and Microsoft's unified security operations model now puts Sentinel and Defender XDR incidents in the same Defender portal queue. Splunk is a capable platform and this page will not pretend otherwise; the trade is between a SIEM you know and one that sits where your telemetry already lives, and the migration is where that trade is either won or wasted. A SIEM migration is not a log migration. It is a detection-content migration with a data-onboarding project attached. IT Partner starts by exporting what Splunk really runs — inputs and forwarders, sourcetypes and indexes, saved searches and Enterprise Security correlation searches, lookups, macros, dashboards, and alert actions — and triaging it with your analysts: which rules fire, which are noise nobody has silenced, which duplicate detections Defender XDR already raises natively, and which are genuinely yours. Every data source is then mapped to a Sentinel connector — Microsoft-native connectors for Defender, Entra, Microsoft 365 and Azure; the Azure Monitor Agent with data collection rules for Windows, syslog, and CEF; Content Hub solutions or codeless connectors for cloud and SaaS APIs — and any source with no supported path is flagged in week one, not at cutover. Detection conversion uses Microsoft's SIEM migration experience, which ingests a Splunk saved-search export, maps rules to out-of-the-box Sentinel analytics or Defender XDR native detections, translates SPL to KQL, converts CIM references to ASIM and lookups to watchlists — and reports a translation state per rule. We treat that output as a draft: every converted rule is reviewed, tested against live data, and given correct entity mapping, MITRE tactics, severity, and grouping; rules the tooling cannot translate are rebuilt from their intent by hand. The fixed three-week window converts an agreed initial set — the sources and detections your analysts rank first, agreed in week one and sized to the window — while the whole export goes through the translation tooling, so the remainder is quoted from a per-rule translation state rather than an estimate. The parallel run is where the promise is proven. The window ends with Sentinel live beside Splunk on the initial set and a first incident-parity reading — what Splunk alerted on that Sentinel did not, and the reverse. The full parallel run, in which both SIEMs ingest the same sources for an agreed window and every divergence is resolved or formally accepted before anything is switched off, follows as a quoted extension together with the remaining sources and detections; nothing is switched off inside the fixed window. Alert routing, ticket creation, and on-call runbooks are rebuilt as Sentinel automation rules and Logic Apps playbooks — for the initial set inside the window — and switched over at cutover, when forwarders are re-pointed source by source and Splunk stays licensed and running because it is the rollback. Historical data is a deliberate decision rather than a default: most firms keep the Splunk indexes read-only through their retention period instead of paying to re-ingest years of logs, and the closeout checklist says exactly when the Splunk contract can safely end. Cost is modeled, not asserted. Sentinel bills on ingestion: an analytics tier priced per GB, commitment tiers that discount reserved daily volume, a lower-cost data lake tier for high-volume logs you keep but rarely query, free ingestion for specific Microsoft sources, and a per-user benefit for Microsoft 365 E5 customers on named tables. The model takes your measured ingest per source, makes a tiering decision per table, uses Microsoft's list prices on the day it is built, and sits beside your Splunk renewal. We will tell you if the answer is not cheaper. What we do not do here is run the SOC afterwards: ongoing triage and response live in Microsoft Sentinel SIEM/SOAR Ongoing Monitoring and, across platforms, Managed Detection and Response.
Success criteria
What you receive
How the work unfolds
Export Splunk configuration and content (inputs, props and transforms, saved searches, Enterprise Security content, lookups, dashboards), pull license usage to measure ingest per sourcetype, run the export through the SIEM migration experience for a translation state per rule, and triage with your analysts: which rules fire, which are noise, which Defender XDR already covers. Agree the initial migration set — the sources and detections that fit the window — the connector map, the workspace and tiering design, the first-pass cost model, and the change windows for forwarder and syslog re-pointing.
Ready the workspace, onboard the initial data sources — native connectors, Azure Monitor Agent and data collection rules, syslog/CEF collection, API connectors — validate ingestion and normalization, review and hand-convert the initial detections, build their watchlists, and test each rule against live data. Automation rules and playbooks reproduce the alert actions kept for those detections; Splunk's own alert actions stay untouched.
Sentinel runs beside Splunk on the initial set and the first incident-parity reading is taken and worked through with your security lead. The cost model is updated with Sentinel's measured ingest; the cutover runbook and rollback, the historical-data decision, and the decommission checklist are delivered; analysts get the Defender-portal walkthrough and the SPL-to-KQL primer; and you receive the written quote for the remainder — full parallel run, remaining sources and detections, cutover.
Under the extension quote: both SIEMs ingest the same sources for the agreed parallel-run window with weekly parity readings, the remaining sources and detections are migrated in priority order, alert routing and ticketing switch to Sentinel, Splunk alert actions are disabled and forwarders redirected source by source within agreed windows with the rollback kept live, and the decommission checklist is executed.
Prerequisites
Who does what
IT Partner
- Lead the Splunk inventory, ingest measurement, and disposition triage with your analysts.
- Design the connector map, workspace and tiering baseline, and the cost model, and keep the model current through closeout.
- Onboard the initial set's data sources and validate ingestion and normalization for every connector in it.
- Convert, review, and test every detection in the initial set; build its watchlists, automation rules, and playbooks to parity.
- Define the parallel-run method and deliver the first incident-parity reading; run the full parallel run and produce the parity report under the extension.
- Write the cutover runbook and rollback and the decommission checklist, deliver knowledge transfer and a written quote for the remainder built from the inventory; execute the cutover under the extension.
- Say plainly, in writing, where Sentinel will not reproduce a Splunk capability one-for-one.
Your team
- Provide Splunk, Azure, and log-source access and the named owners for each source.
- Agree the initial migration set in week one, decide the disposition of each detection, and accept or reject parity gaps within the agreed turnaround.
- Approve the tiering design, the commitment-tier decision, the extension quote, and each cutover window.
- Keep Splunk licensed through cutover verification and own the commercial relationship and termination timing with Splunk.
- Attend the parity readings and the analyst working sessions.
- Operate Sentinel after handoff, or contract ongoing monitoring separately.
What's not included
Limitations & technical notes
Frequently asked questions
Is Microsoft Sentinel cheaper than Splunk?
Sometimes substantially, sometimes not, and the honest answer depends on your ingest mix. Sentinel bills per GB ingested into the analytics tier, discounts reserved daily volume through commitment tiers, offers a lower-cost data lake tier for high-volume logs you keep but rarely query, and ingests certain Microsoft sources — Office 365 audit, Azure Activity, Defender alerts — at no charge, plus a per-user benefit for Microsoft 365 E5 customers on specific tables. A Microsoft-heavy estate often lands well below its Splunk renewal; an estate dominated by firewall and application logs may not. That is why the cost model is built from your measured ingest, per source, with tiering decisions, and shown beside the renewal — and why we will tell you if the answer is 'not cheaper.'
What does Microsoft's SIEM migration tool actually do — and what does it not?
It takes a CSV export of your Splunk saved searches, analyzes each rule's intent, and recommends either a matching out-of-the-box Sentinel analytics rule or a Defender XDR native detection, or translates the SPL to KQL directly. It maps Splunk sources to Sentinel tables, lookups to watchlists, macros inline, and Common Information Model fields to ASIM. What it does not do is guarantee correctness: it reports a translation state per rule, and complex joins, custom macros, and Enterprise Security risk-based alerting typically come out partial. We treat every output as a draft to be reviewed and tested against live data, and rebuild the remainder by hand.
Will we lose detections in the move?
Not silently. Every Splunk rule gets a recorded disposition — converted, replaced by a native detection, or retired with a reason — and the parallel run compares real incidents between the two platforms until the gaps are closed or formally accepted by your security lead. What you may lose on purpose are rules that never fired, duplicated Defender's own detections, or alerted on noise nobody triaged; the inventory tends to be the first honest audit of a Splunk rule base in years.
What fits in the three-week window, and what is quoted separately?
The window is fixed and its scope is agreed in writing in week one. Inside it: the full Splunk inventory with a disposition per item, the connector map for every source, the workspace and tiering design, the initial migration set — the sources and detections your analysts rank first, sized to fit the window — converted, tested, and live in Sentinel beside Splunk, the first incident-parity reading, the cost model, the cutover runbook and decommission checklist, and knowledge transfer. Quoted separately, from that inventory: the full parallel-run window, the remaining sources and detections, cutover execution, decommissioning, and any historical re-ingest. Nothing is switched off inside the window, so if you stop after it you have a working Sentinel on your highest-value sources and a priced plan — not a half-finished migration.
What happens to years of historical data in Splunk?
It usually stays where it is. Re-ingesting archives into Sentinel means paying ingestion on data you already paid for once, so most firms keep the Splunk indexes read-only through their retention period, document that decision against their compliance obligations, and let it age out. Where a subset genuinely must be queryable in Sentinel, an export and re-ingest is scoped separately. The decommission checklist makes sure nobody cancels Splunk before the retention question is answered.
How long do both SIEMs run in parallel, and what does that cost?
The fixed window ends with Sentinel live beside Splunk on the initial set and a first incident-parity reading; the full parallel run — both SIEMs ingesting the same sources, compared incident by incident until the gaps are closed or accepted — is quoted as an extension, with a window agreed from that reading and extendable when parity evidence says so. Throughout, you pay Splunk as usual and Microsoft for Sentinel ingestion of the same sources — the cost model shows the overlap explicitly. It is the price of a cutover you can defend; a big-bang switch without a parity report is cheaper for exactly as long as nothing goes wrong.
Do we need Microsoft 365 E5 or Defender XDR for this to make sense?
No, but they change the economics. Defender for Endpoint, Identity, Office 365, and Cloud Apps feed Sentinel through native connectors with alerts ingested free, and the Microsoft 365 E5 benefit adds a daily per-user ingestion allowance on named tables. An estate without those products still migrates; it just leans harder on syslog, CEF, and API sources, which are all priced ingestion. The cost model shows both realities against your actual licensing.
Our analysts know SPL, not KQL. How does that go?
Better than most expect. KQL is a pipeline language too, and the converted rules from your own environment double as a translation guide — the knowledge transfer uses them as the primer. The window includes working sessions where analysts hunt in KQL against live data with us on the call, and the tuning backlog they inherit is written in their new language, not ours.
We run Splunk Enterprise Security. Do correlation searches, notable events, and risk-based alerting carry over?
Correlation searches convert like any saved search, with the multi-source ones more often rebuilt than translated. Notable events map to Sentinel incidents with grouping and entity mapping; risk-based alerting has no direct equivalent and is redesigned as a combination of analytics rules, entity-based incident correlation, and Defender XDR's own correlation. The inventory calls out each ES construct and its Sentinel design so nothing is assumed to be a straight port.
What about our Splunk dashboards and apps?
Operational views your analysts use daily are rebuilt as Sentinel workbooks — those are in scope. Vendor apps are generally replaced by the corresponding Content Hub solution, which ships its own parsers, rules, and workbooks. Dashboards nobody has opened in a year are retired, and the inventory will show you which is which.
Do you build in the Azure portal or the Defender portal?
The Defender portal. Microsoft has announced the retirement of Sentinel's Azure-portal experience (currently scheduled for March 2027 at the time of writing) and its unified security operations model puts Sentinel and Defender XDR incidents, hunting, and automation in one queue. The Log Analytics workspace remains the data store and the billing object underneath, so nothing about ingestion or cost changes — only where your analysts work.
Do you run our SOC after the migration?
Not inside this project — the migration ends with cutover, a parity report, and a team that can operate Sentinel. Ongoing monitoring, triage, and response are separate recurring services: Microsoft Sentinel SIEM/SOAR Ongoing Monitoring for the Sentinel estate, or Managed Detection and Response when you want coverage across Microsoft and non-Microsoft platforms. Keeping the two separate keeps the migration honest about what it did and did not fix.
We are on QRadar, ArcSight, or another SIEM — is this the same service?
The method is identical — inventory, connector map, rule conversion, parallel run, cutover, cost model — and we quote those migrations on request. What differs is the tooling: Microsoft's automated rule translation targets Splunk, so more of the detection conversion is engineered by hand and the quote reflects it.
Why is there no price on the page?
Because a ten-source, forty-rule estate and a two-hundred-source, six-hundred-rule Enterprise Security deployment are different projects, and one number would be wrong for both. The fixed three-week window is quoted per estate; the extension — full parallel run, remaining content, cutover — is quoted from the inventory the window produces. Scoping is quick: your license usage report and a saved-search count get you the written quote, and per our standard terms you pay after you approve delivery. Azure consumption is separate and projected transparently in the cost model.
When can we safely cancel Splunk?
After cutover is verified, the parity report is closed, and the historical-data decision is executed — and not a day before, because a live Splunk is the rollback during the cutover window. The decommission checklist puts those gates in order alongside your contract dates so the cancellation is a scheduled step rather than a leap.