migrate tool doesn't work when the source dir is readonly

[VenkateswaranJ]

migrate -source.config.file=/alloc/loki-config.yaml -dest.config.file=config-dst.yaml -from=2025-02-17T00:00:00Z -to=2025-02-19T00:00:00Z

2025-02-18 15:26:13.150169 I | listen tcp 127.0.0.1:8080: bind: address already in use
2025-02-18 15:26:13.193044 I | With a shard duration of 6h0m0s, 7 ranges have been calculated.
2025-02-18 15:26:13.193255 I | Received done call
2025-02-18 15:26:13.193279 I | Waiting for threads to exit
2025-02-18 15:26:13.193374 I | 4 Error querying index for chunk refs: mkdir /mnt/loki_storage/tsdb-shipper-cache/index_20136: read-only file system
2025-02-18 15:26:13.193395 I | 3 Finished processing sync range 7 of 7 - Start: 2025-02-18 18:00:00.000000001 +0000 UTC, End: 2025-02-19 00:00:00 +0000 UTC, 0 chunks, 0 B in 0.0 seconds 0 B/second
2025-02-18 15:26:13.193411 I | 3 Requested to be done, context cancelled, quitting.
2025-02-18 15:26:13.193490 I | 5 Error querying index for chunk refs: mkdir /mnt/loki_storage/tsdb-shipper-cache/index_20136: read-only file system
2025-02-18 15:26:13.193558 I | 7 Error querying index for chunk refs: mkdir /mnt/loki_storage/tsdb-shipper-cache/index_20136: read-only file system
2025-02-18 15:26:13.193617 I | 6 Error querying index for chunk refs: mkdir /mnt/loki_storage/tsdb-shipper-cache/index_20136: read-only file system
2025-02-18 15:26:13.193770 I | 1 Finished processing sync range 4 of 7 - Start: 2025-02-18 00:00:00.000000001 +0000 UTC, End: 2025-02-18 06:00:00 +0000 UTC, 0 chunks, 0 B in 0.0 seconds 0 B/second
2025-02-18 15:26:13.193788 I | 1 Requested to be done, context cancelled, quitting.
2025-02-18 15:26:13.681450 I | 0 Finished processing sync range 5 of 7 - Start: 2025-02-18 06:00:00.000000001 +0000 UTC, End: 2025-02-18 12:00:00 +0000 UTC, 68 chunks, 821.4 kB in 0.5 seconds 1.7 MB/second
2025-02-18 15:26:13.681467 I | 0 Requested to be done, context cancelled, quitting.
2025-02-18 15:26:13.692474 I | 2 Finished processing sync range 6 of 7 - Start: 2025-02-18 12:00:00.000000001 +0000 UTC, End: 2025-02-18 18:00:00 +0000 UTC, 73 chunks, 1.6 MB in 0.5 seconds 3.1 MB/second
2025-02-18 15:26:13.692509 I | 2 Requested to be done, context cancelled, quitting.

Loki version - 3.3.2 (migrate tool also compiled from the same branch)

I wonder why the migrate tool trying to write something to the source dir /mnt/loki_storage/tsdb-shipper-cache/? I thought it only read from the loki path of -source.config.file

Error querying index for chunk refs: mkdir /mnt/loki_storage/tsdb-shipper-cache/index_20136: read-only file system